Figure 21-01 Twin diesels being installed in a big Sea Ray. Note the Onan generator forward of the engines. The boat’s future owner will never enjoy the degree of engine-room access that this worker has right now.
Gasoline and Diesel Inboard Engines • Pod Drives Inboard and Outboard Engine Maintenance
For optimal performance, utility, and safety, a boat’s propulsion package should match its type, size, and intended purpose. Small trailerable boats, for example, are typically powered by outboards or sterndrives, also called inboardoutboards and IOs. Center-console fishing boats are generally driven by outboards, while fishing boats with cabins use outboards or twin gasoline inboards up to roughly 40 feet and diesel inboards beyond that. Most ski boats use gasoline inboards, while trawlers and large motoryachts are almost always propelled by diesel inboards. Daysailers and small cruising sailboats of less than about 25 feet typically rely on an outboard with a long shaft, either affixed to a transom-mounted bracket or mounted in a cockpit well, while larger sailboats usually have a small inboard diesel.
As both fuel and boats have gotten more expensive, diesel engines have become more competitive with gasoline engines. New electronically controlled diesels are lighter, quieter, more powerful and fuel-efficient, and less polluting than engines of just a decade ago. At the same time, mandated pollution-control equipment such as electronic fuel injection and catalytic converters have made gasoline engines more expensive, reducing (but not eliminating) their cost advantage over diesels.
Figure 21-02 A 25-hp four-stroke outboard (a popular size) with electronic fuel injection is a quiet, fuel-efficient propulsion system for this 13-foot boat.
There are three main drive-system options for gasoline and diesel inboards, the most familiar of which employs a conventional straight drive shaft that runs aft from the engine and exits through the bottom of the hull at a descending angle. Outside the hull it is usually supported by an exterior strut mounted to the hull bottom. A propeller is fixed to the shaft end via two large locking nuts. Steering is accomplished by a rudder mounted behind the prop; the drive shaft itself, being fixed, can provide no steering ability. Reverse propulsion is accomplished by means of a marine transmission, which reverses the direction of drive shaft and propeller rotation.
Figure 21-03 Outboard-driven boats are commonly smaller than inboard-engine boats, but not always. Three 350-hp outboards can get this big center-console boat out to the best fishing grounds in a hurry.
A waterjet uses a powerful pump inside the boat that is connected to the engine by a short drive shaft. The pump impeller generates a stream of high-pressure water that exits the back of the boat through a steerable nozzle, providing steering ability as well as propulsion and thus eliminating the need for a rudder or rudders. When the operator calls for reverse propulsion power, an articulated DIVERTER, commonly called a “bucket,” deploys into the high-pressure stream, essentially reversing its direction. Without rudders and external struts, shafts, and propellers, jet-drive boats experience much less drag than boats with conventional drives, and they can have shallower draft. They will not foul lobster pots and other fishing gear, and they are safer to operate around swimmers. Jet-drive boats are discussed in Chapter 7.
Figure 21-04 Twin Hamilton Waterjets power the Hinckley T34. The buckets, or diverters, are clearly visible.
A sterndrive has the engine inside the boat and the outdrive, a steerable component containing the propeller, mounted on the outside of the transom. In a conventional twin-sterndrive application—as discussed in Chapter 7—both outdrives move in unison, but new microprocessorcontrolled systems allow each drive to operate independently; a helm-mounted joystick sends inputs to the microprocessor, giving the helmsman what is basically “point-and-shoot” operation.
Joystick operation is available for larger boats, too, thanks to pod drives—Volvo Penta’s IPS and Cummins' Zeus—which feature independently controlled propeller pods mounted aft on the bottom of the hull and a microprocessor that reacts to movement of the wheel or joystick. For more information on pod drives, see page 755. Joystick controls for conventional straight drive systems with electric thrusters are available from Cummins, ZF Marine, and Twin Disc.
Figure 21-05 Left: An express cruiser demonstrates the superb maneuverability of MerCruiser’s joystick-controlled, independently articulating Axius sterndrive system. Right: The Axius system joystick operates two sterndrives independently via computer control, enabling impressively tight and precise dockside maneuvering. The system responds both to the direction you move the joystick and the pressure you apply. For comparisons of outboard and sterndrive engines, and for information on handling outboard- and sterndrive-powered boats, see Chapter 7.
Outboard and sterndrive engine selection and operation are discussed in Chapter 7. Among other topics, Chapter 7 considers outboard versus sterndrive engines for small boats, two-stroke versus four-stroke outboards, and the uses of small electric trolling motors. Also discussed there are propeller design and materials, outboard-engine fuels and fueling, and outboard engine controls and adjustments.
In this chapter we discuss gasoline and diesel inboard engines for boats roughly 25 feet and larger, and then present common troubleshooting and maintenance procedures for all engines.
Figure 21-06 A two-shaft marine transmission. In forward gear, the input shaft (from the engine crankshaft) engages directly with the output shaft. In reverse gear, however, the input torque is transferred to the output shaft indirectly via an intermediate gear, which reverses the output shaft rotation.
GASOLINE & DIESEL INBOARD ENGINES
Gasoline inboard engines are typically automotive engines that have been “marinized”; that is, they have been equipped with cooling systems and water-jacketed exhaust manifolds that use the water surrounding the boat to remove heat. Operationally they are basically identical to car engines, but instead of being connected to a multispeed transmission, they mount to a marine transmission, or marine gear, which has only forward, neutral, and reverse and a fixed reduction ratio. A marine gear has an internal oil pump powered off the engine that uses hydraulic pressure to compress a series of internal clutches that in turn provide engagement (forward or reverse) and disengagement (neutral). A marine gear’s forward end typically mounts directly to the engine, and its aft end has an output flange that bolts to the propeller shaft, sterndrive, pod, or waterjet pump. The location of the engine or engines depends largely on the type of drive system.
Figure 21-07 A cruising sailboat approaches a tucked-away dock in the San Juan Islands under power, fenders deployed for a port-side landing, line handlers at their posts forward, aft, and amidships. A good crew, calm day, and open dock make docking a pleasure. An auxiliary sailboat of this size might be powered by a 30- to 50-hp diesel. The powerboat at the dock is a Sabre 42 flybridge cruiser with twin diesel engines (Cummins QSB 425 hp) powering Zeus pod drives.
Modern marine diesels may be either marinizations of industrial (usually truck) engines or engines designed from the start for boats, usually commercial vessels. Marine diesels use marine gears that are identical in design to those for gasoline engines but of much heavier construction.
One variation of the inboard is the V-drive, in which the engine is mounted backwards. A short drive shaft (“jackshaft”) leads from the marine gear on the front of the engine to the input end of the V-drive; the V-drive’s output end is pointed 180 degrees in the opposite direction so that the propeller shaft connecting to it passes under the engine. While the V-drive gear creates some frictional loss, this setup allows the engine to be mounted as much as four feet farther aft, saving space, and with the weight of the engine and running gear farther aft, the boat usually gets on plane easier. V-drives are most often used in cruising boats because of the extra interior space they produce. They are usually unsuitable for fishing boats, as the engines and gears occupy space that would normally be taken up by bait wells and fish boxes.
Figure 21-08 Two views of a Twin Disc V-drive marine transmission.
In a typical inboard installation—whether straight-shaft or V-drive—the shaft and prop are fixed; they can’t be turned to steer the boat. These inboard boats need rudders for steerage, and they, along with shafts and struts, produce considerable underwater drag. Such drag is reduced in sterndrives, waterjets, and pod drives.
GASOLINE OR DIESEL?
Gasoline inboard engines are lighter and less expensive to purchase and maintain than diesels of comparable power, and while they burn about a third more fuel per horsepower, they typically produce faster acceleration. However, diesels can be safely run continuously at 80 to 90 percent of full throttle, while gasoline engines should be run at around 65 percent. Consequently, diesels usually produce equivalent or higher cruising speeds. Diesels also produce more torque—the twisting force that drives the propeller—at lower speeds, so they are better for heavy boats.
For a variety of reasons—including the use of heavier materials, the fact that their fuel is actually oil and so lubricates as it provides power, and that they run at slower speeds than gasoline engines—diesels typically have a longer life—three or four times as long—between rebuilds. Still, the life of a well-maintained gasoline inboard engine is measured in thousands of hours of operation, and the costs of standard annual maintenance are less than for a diesel because, for a typical oil change, the diesel requires three or four times as much oil and has more, and more expensive, filters. Traditionally, diesel engines enjoyed the advantage of not requiring tune-ups as gasoline engines did, but modern electronic gasoline engines no longer require frequent tune-ups. Diesels are typically more reliable than gasoline engines (although new gasoline models are closing the gap), mainly because they do not have the electrical system necessary to produce a spark to initiate ignition.
Finally, since gasoline is highly volatile, it produces fumes that can explode. Under normal circumstances diesel fuel produces no explosive vapors and will burn only if exposed to a flame or, when atomized, to a spark; it is highly unlikely to explode. That’s why it’s so important to run the bilge blower of a gasoline-powered boat before starting the engines. (Not a bad idea for diesels too, just to be safe.)
Figure 21-09 This Sabre 34 hardtop express cruiser is powered by twin 315-hp Yanmar diesels. Note the modified-V planing hull with running strakes and chine step. The deadrise is 23° amidships, 16° at the transom. (Refer to Chapter 1 for more on the modified-V hull shape, chines, and deadrise.) This boat will run at 26 knots with engines turning at 3,600 rpm while burning approximately 30 gallons of fuel per hour.
Inboard-Engine Cooling Systems
In gasoline and diesel engines—as in car and truck engines—the cylinders are surrounded by spaces in which coolant—in most cases a 50/50 mix of fresh water (distilled is better) and antifreeze—is circulated in a closed loop by an engine-mounted pump. In a car or truck, heat is removed from coolant by passing it through a water-to-air heat exchanger—a radiator. Basically the coolant passes through small tubes over which air passes as the vehicle moves. In boats, heat is removed from coolant by a water-towater heat exchanger; this can be in the form of an internal heat exchanger through which raw water is circulated or a KEEL COOLER, which is basically piping mounted to the outside of the hull underbody. Keel coolers are often preferred by long-range cruising boats because of their simplicity and reduced likelihood of corrosion, but they add underwater drag (not an important factor in a slow displacement boat) and can snag lines or debris.
In the case of an internal heat exchanger, the coolant circulates through small tubes, as in an automobile, but is exposed to water drawn in from outside the boat rather than to flowing air. To do this, a marine engine requires a second pump—a RAW-WATER PUMP—to pull water from outside the boat and force it through the heat exchanger and back out of the boat. This pump contains a flexible multi-vaned rubber impeller that is susceptible to damage from water-borne debris and wear, so before the water reaches the pump, it passes through a strainer mounted either inside or outside the boat that removes foreign material that could not only damage the impeller but also clog tiny heat-exchanger passages.
Once the water leaves the internal heat exchanger, it is injected into the exhaust manifold, usually at its highest point, where it combines with exhaust gases, cooling them to a safe temperature, and then is pushed through the muffler and out the exhaust outlet. (A boat equipped with a keel cooler will have a separate raw-water system to do this.) When you start your inboard engine, you should look at the exhaust outlet to make sure water is coming out; if it’s not, your raw-water pump is faulty, and if the engine continues to run, it will overheat. Similarly, if your engine temperature gauge begins to rise during operation, you should again check the water flow out of the exhaust(s) before doing anything else. If it is a mere trickle or has stopped altogether, look for an obstruction at the raw-water intake—a plastic bag or grass or seaweed—clogging the internal strainer. (Most strainers are made of clear glass, so you can check this visually.)
A few inboards and most outboards are “raw-water-cooled,” meaning they do not have a heat exchanger or recirculating fresh water. In inboards this can lead to internal corrosion if the boat is operated in salt water. This is not typically a problem with outboards because they are made of aluminum alloy, although many outboard manufacturers recommend freshwater flushing after use.
DIESEL ENGINES
Diesel engines have been gaining popularity in recreational marine use over the past two or three decades as fuel and boat prices have increased. But they’ve been around since 1892, when Rudolph Diesel, a German engineer, patented an engine that used hot compressed air to ignite fine coal dust. (His previous attempt had blown up.) Today diesels are considered safer than gasoline engines because gasoline is much more volatile and flammable and because a diesel engine does not have a high-voltage electrical system that can create sparks.
The operation of a diesel engine is surprisingly simple. Fuel is injected into each cylinder via a nozzle, or INJECTOR, which turns it into a fine mist. Because a diesel engine has a much higher compression ratio than a gasoline engine, sufficient heat is generated by the piston compressing the air on its upstroke to ignite the fuel-air mixture without the aid of a spark plug. When the fuel injector sprays a very fine mist into the cylinder, the mixture ignites, expands, and drives the piston downward, turning the crankshaft. (The combustion process for a gasoline engine is similar except that in some older engines, a carburetor mixes the air and fuel, and since its compression ratio is only about 60 percent that of a diesel, a spark plug is required to ignite the mixture.)
Figure 21-10 This 27-foot Ranger Tug has above-the-water styling reminiscent of a tugboat, but the resemblance ends at the waterline. The boat will reach 20-knot speeds with its single 180-hp Yanmar diesel and can cruise at 15 knots, and its 8°-foot beam and 6,200-pound unloaded displacement enable it to be trailered.
Figure 21-11 The Grand Banks 36 is meant for comfortable running at displacement speeds, so power can be modest. This boat’s twin 135-hp Ford Lehman diesels identify it as an older model, since Ford Lehmans have not been available for some years, although parts are readily available. Some Grand Banks 36’s are powered by single engines.
GASOLINE FUEL AND ETHANOL
Beginning around 2000, many states, and eventually the federal government, mandated that ethanol be mixed with gasoline to reduce emissions, boost octane, protect the environment, and help farmers. (Most ethanol is made from corn.) The federal government specified a mixture of 10 percent ethanol to 90 percent gasoline called E10. Since then most boat owners have used E10 without significant problems, though some say it has damaged their fuel tanks and fuel-system components (particularly those made of synthetic rubber) and even caused inboards and outboards to misfire, overheat, or shut down.
Besides being a fuel, ethanol is also a solvent that can loosen varnish and gum, and even rust, that has accumulated in fuel tanks, sending contaminants through the fuel system where they clog filters and carburetors or fuel injectors. Ethanol also degrades the epoxy and polyester resins that were used in many fiberglass tanks up until the early 1990s, causing them to soften and, at worst, leak fuel into the bilge. Tanks made with vinylester resins are not affected.
To make matters worse, ethanol is hygroscopic, meaning that it attracts water. The higher the humidity, the more water ethanol will pull put of the air. The resulting gasoline-water mixture forms layers in a process called phase separation—gasoline on top, water and ethanol on the bottom, which is where the fuel pickup is. Once water is drawn into the engine, it can reduce the lubrication efficiency of oil, causing increased wear and reducing engine life. Because it dilutes gasoline, water also results in poor performance.
Most boaters, even those with older boats, can mitigate or negate these effects by using a fuel stabilizer recommended by the engine manufacturer and by installing a fuel-water separator in the fuel line to remove water. If you suspect your boat is susceptible to ethanolrelated contamination, change your fuel filter(s) often—every 50 to 100 hours—and keep spares on board in case one clogs while you’re underway. (You may need a 10-micron filter to trap all the sludge.) Periodically check all fuel system components that are susceptible—the rubber primer bulb, rubber fuel lines, fuel filter, fuel pump, hoses, gaskets, and tanks. Finally, keep your fuel tank full as much as possible and make sure the filler cap seals tightly to prevent condensation from forming inside the tank. When you store the boat for the off-season, either remove all fuel from the tank or fill it and add a fuel stabilizer.
E10 is not usually a problem for engines built after 1991, and today most engine manufacturers regard it as an acceptable fuel. In 2008, however, ethanol manufacturers asked the federal government to replace E10 with E15—15 percent ethanol and 85 percent gasoline. After some tests, engine manufacturers and the National Marine Manufacturers Association objected to the 50-percent increase, saying it would lead to overheating, piston deterioration, and even catastrophic failures. Test results released in late 2011 by the U.S. Department of Energy supported these claims. In 2009 the Environmental Protection Agency issued a waiver for E15, effectively allowing it into the fuel supply, but did not mandate E15 use. In August 2012, a U.S. Court of Appeals rejected a boating industry challenge to the EPA waiver. The NMMA has distributed warning labels to boat manufacturers across the U.S. in the hope that these would be placed on all new boats. The labels alert boaters to the potential dangers of E15 and warn against use of the fuel.
Diesel Air & Fuel
Diesels need two things: large amounts of clean air and, because fuel injector passages are so tiny (in order to create that fine mist), very clean fuel. A typical mid-size diesel needs about 1,500 cubic feet of air per gallon of fuel. To make sure it’s free of contaminants, most modern diesels have a combination air filter/intake silencer with an element that must be periodically cleaned or replaced. As for fuel, all diesels are equipped with at least one engine-mounted fuel filter designed to remove particulate matter and small amounts of water. It should be replaced when the engine is serviced. (See your owner’s manual for specifics.) In addition, most diesel-powered boats today have a separate auxiliary fuel filter called a fuelwater separator that is mounted off the engine. It contains a fine-particulate filter element—typically one that can trap particles down to 10 microns—that also needs to be periodically replaced and internal vanes that spin the fuel like a centrifuge to separate heavier water from fuel. Water accumulates in a settling bowl (usually made of a clear material so you can see it) on the bottom of the separator. When it’s visible (it is a lighter color than fuel), it must be drained via a petcock on the bottom of the bowl. The principal advantage of a fuel-water separator is that it can handle much larger amounts of water than the engine-mounted filter before requiring servicing.
Figure 21-12 A sea strainer like this internal one, mounted between the raw-water intake and the raw-water pump, removes detritus that might otherwise damage the pump impeller or clog the heat-exchanger passages.
To help prevent water from getting into the diesel fuel in your boat’s tanks, make sure the fuel fill cap is snug and tight so that rain and washdown water can’t drip into the tank. Check the cap’s gasket periodically, and replace it if it’s worn or cracked. If you see droplets of water on the underside of the cap, condensation may be forming inside the tank. Keeping your tank(s) as full as possible at all times will help minimize condensation. Whenever possible, buy your fuel from a reliable, reputable source so that it doesn’t already have moisture and contaminants in it when it comes aboard.
Figure 21-13 A dual fuel-water separator with vacuum gauge for a diesel fuel system.
Water in diesel fuel—whether from poor-quality fuel or condensation—can cause misfiring in small amounts and outright stoppage in larger ones; it can also cause corrosion and the growth of an algae-like substance in fuel tanks, which can be very difficult (and costly) to remove. This material typically accumulates on the bottom of the tank and is stirred up when the fuel is agitated—as in rough seas. Even a top-quality fuel-water separator can handle only a small amount of this sludge before it becomes clogged and your engine stops. When that happens, you’ll need to replace the element in the fuel-water separator, which has prevented the sludge from reaching the engine-mounted filter(s). Unfortunately, replacing the element can be very difficult and messy in a seaway, and if there is a sizable accumulation of sludge in the tank, the new element will quickly clog and your engine will stop again.
One option worth considering is dual separators. The engine runs off one until it becomes contaminated, at which point, by throwing a lever, you can switch the engine to the other one without missing a beat. You can then change the dirty element on the off-line separator without stopping the engine. A second option, a vacuum gauge, can show at a glance when the filter element is getting clogged, so you won’t have to wait for the engine to lose power, surge, or miss before changing elements.
One problem you’ll face whenever you service your diesel’s fuel system is air being introduced into the fuel system. Any air will stop a diesel engine. It is most often introduced when someone changes a fuel filter and fails to top off the filter fully with clean fuel. Bleeding air out of a diesel’s fuel system is a complex, time-consuming process that often requires loosening a fitting so the air can escape. Procedures vary from engine to engine (check your engine manual), but regardless, this is not something you want to learn on the spot. Spending a few minutes reviewing the procedure at dockside will save you a lot of time and frustration when things go awry.
Figure 21-14 A six-cylinder common-rail diesel engine producing 270 to 350 hp and topping out at 3,800 rpm.
Common Diesel Engine Terms
NATURALLY ASPIRATED A diesel engine that is not turbocharged. The amount of air entering the engine depends solely on the vacuum created by the downward-traveling pistons.
TURBOCHARGED A diesel engine fitted with an air pump powered by exhaust gases that forces more air into the cylinders than natural aspiration would provide. This allows more fuel to be added, creating more horsepower.
INTERCOOLER or AFTERCOOLER A radiatorlike device between the turbocharger outlet and the engine air intake. Turbocharging compresses air, raising its temperature and making it less dense and thus reducing the benefits of turbocharging. An aftercooler or intercooler (they are basically identical) uses engine coolant to lower the intake air temperature, allowing more air into the engine and thus more fuel to be added, creating more horsepower.
COMMON-RAIL DIESEL A diesel in which all of the fuel injectors are connected via a single tube containing diesel fuel under extremely high pressure—around 30,000 pounds per square inch. This allows the use of electronically controlled fuel injectors with extremely small holes that create an ultra-fine mist of fuel, which burns faster and more completely.
With a traditional (non-common-rail) injector, there is often a lag time between when the pump generates injection pressure and the actual injection; in addition, the volume of fuel in the injection line at any given time is relatively small, particularly at lower loads. The common-rail system minimizes lag, leading to faster acceleration and better throttle response. It also is more efficient over the entire power range and produces less smoke, noise, and vibration. The downside is that it depends on very sophisticated electronics and, because of the high pressure involved, can be serviced only by trained mechanics.
POD DRIVES
Azipod drives have been used in commercial vessels such as cruise ships and tugboats—and even a few megayachts—for a long time, but have been installed in smaller pleasure craft only since 2004, when Volvo Penta introduced its IPS (Inboard Performance System). They quickly became popular for a variety of reasons. Each drive operates independently and can change propeller thrust through a wide arc (though less than 180 degrees), yielding much faster response to helm input than with a conventional inboard. Since the drives are controlled by a microprocessor, the system always positions the pods in the optimum position. If equipped with an optional joystick control, a helmsman need only point the boat where he wants it to go, and the boat will go there—even moving directly sideways—without the aid of bow and stern thrusters. IPS and Zeus, a competing system from Cummins that followed in short order, both use counter-rotating propellers, which improve efficiency. The Zeus drive is now offered with Caterpillar engines, and the ZF drive with Yanmar engines.
An azipod drive system eliminates much of the running gear—the prop shafts, struts, and rudders—of a conventional drive system, thus reducing drag. Azipod propellers are mounted roughly parallel to the keel, not inclined as in an inboard. Thus, no thrust is wasted.
An underwater look at aft-facing pod drives mounted in shallow tunnels to reduce draft. Note the seal next to the hull so that the drive leg will break away in case of a catastrophic grounding.
Finally, because the azipod relies on two 90-degree gear sets to transmit power to the propeller, it’s much more compact than an inboard using an angled drive shaft. An azipod system typically places the engines three feet farther aft, which frees up interior space and enhances planing. Azipods are also much easier for a manufacturer to install. There are no hydraulics or cabling; everything for the control system is contained in a wiring harness. Moreover, the exhaust system is typically internal to the drive and doesn’t require a separate installation, and there is no need for aligning a prop shaft.
Pods are usually used in multiple-engine installations, principally in boats 35 feet long and longer. Most pods are driven by diesel engines, though Volvo Penta also offers gasoline-driven pods.
A Zeus pod unit showing the vertical drive leg coming down through the hull from the transmission and the counter-rotating props protected by a nose cone and small skeg.
The lower portion of an azipod is designed to shear off when striking an object, leaving most of the upper unit intact so that watertight integrity is not compromised.
IPS uses two forward-facing counterrotating propellers, a design Volvo claims exposes the propellers to clean, undisturbed water. Thus IPS is a TRACTOR DRIVE, pulling the boat through the water. Zeus also uses counter-rotating propellers, but they face aft and push the boat in a more conventional fashion.
In addition to joystick handling around docks, pods also offer greater maneuverability at speed because they change the direction of thrust instead of sending it directly aft to be deflected off a rudder blade. Because the control system is electronic, steering ratios and helm feedback can be adjusted to suit a particular installation. Azipod props are typically smaller than the props in an equivalent straight-shaft drive because there are twice as many props and blades; a smaller prop usually means less drag and often a shallower draft.
Though initially designed mainly for twinengine installations, pods have been used in triple- or even quadruple-engine applications on large yachts. ZF Marine has developed a single-engine pod drive for use on smaller boats. Azipod systems can also be integrated with a separate GPS to allow automated station holding, something that is particularly valuable when waiting for a bridge to open or for a berth at a busy fuel dock.
But for all their sophistication, azipod systems do have drawbacks. They are significantly more costly and more complex than a conventional straight-shaft inboard drive system, which is simple, durable, and about as foolproof as anything on a boat can be.
ENGINE MAINTENANCE
Marine engines of all types manufactured in the last decade require much less maintenance than older engines. This is due mainly to electronic engine controls that have been mandated as part of pollution-control regulations. In gasoline engines, such troublesome components as the carburetor, ignition points, and condenser are gone, and even spark plugs now last much longer. And because all marine engines—gasoline and diesel—enjoy much more complete combustion than in the past, engine oil life has been extended.
All this is good news, but it’s wise to remember that marine engines operate under much heavier loads than automotive engines, and this added strain makes even the reduced maintenance requirements of the newest engines critical. Also, the possibility of encountering contaminated fuel—especially water in diesel—adds to the importance of timely maintenance.
There are only three main types of marine engines—gasoline inboard, gasoline outboard, and diesel inboard—but there are many recommended maintenance routines. This is because the age of an engine (among other factors) influences its particular maintenance regimen. That’s why it’s always wise to rely on the documentation that came with your engine and/or the engine manufacturer’s recommendations.
Inboard Engine Maintenance
Most of the following procedures are common to all inboard engines, gasoline and diesel. Steps that are specific to either gas or diesel are noted as they apply.
Daily Checks
Proper maintenance of any inboard engine starts each time you step aboard and before you head out. Performing a few daily checks will allow you to catch any minor problems before they become major ones. Key procedures include:
• Open the engine compartment or engine room and check for the odor of fuel. If you smell it, don’t do anything else until you find its source.
• Make sure the raw-water intake seacock is open. (Closing it each time you leave the boat will prevent problems associated with a leaking hose or broken hose clamp.)
• Check the engine oil level.
• Check the coolant level. Don’t just look at the plastic expansion bottle on the bulkhead; remove the pressure cap on the engine and dip your finger into the tank. If it comes up dry, add a 50-50 mixture of coolant and water until you can just wet the end of your finger. (Never remove the pressure cap when the engine is heated.)
• Inspect all belts for looseness or wear. If you can deflect a belt more than a half-inch, it probably needs tightening.
• Check the bilges for water or oil. If you see either, find the source.
• Check hoses for leaks or cracks. Squeeze them; they should be firm. If they’re soft, they should be replaced.
• Check hose clamps for rust and for looseness with a screwdriver. (All hose connections below the waterline should be double-clamped.)
• If you have a diesel engine with a fuel-water separator, check the clear bowl on the bottom for water. (It will be lighter than the amber diesel fuel.)
• Check your battery connection. Cable connections should be tight and free of corrosion.
Operation
Modern marine engines do not need to be warmed up. Start your engines and let them idle as you remove lines. (Do not gun the engines when you start them.) Unless you have a very short passage to open water, normal slow-speed harbor operation will be enough to sufficiently warm the engines. When you are ready to increase speed, advance the throttles slowly until you reach cruising speed. When you return, there is no need to cool down your engines. Normal idle speed back to the dock will be sufficient. Idling your boat for an extended period at dockside not only wastes fuel and produces pollution, it’s bad for the engines. All internal combustion engines operate most efficiently when under load.
Basic Maintenance
Again, the best source of service information is your engine manual. That said, here are some general guidelines:
• Replace spark plugs annually (gasoline only).
• Change the oil and oil filter every 100 hours (or as recommended in your engine manual) and prior to winter layup.
• Change the fuel filter annually (gasoline only). Diesel fuel filters should be changed at the same time as oil filters.
• Change the transmission oil annually.
• Clean the air intake filter/silencer annually.
• Replace the coolant every three years or 300 hours.
• Check all sacrificial anodes (zincs) every six months, and replace any that are more than half gone. Don’t forget the ones on the transmission oil cooler.
• If your gasoline engine is equipped with a distributor rotor and cap, ignition points, and condenser, replace these annually.
• Check the engine mounts for loose bolts and corrosion.
• For sterndrives, check the lower-unit oil.
Make sure the level is correct, and look for cloudiness, a sign of water intrusion.
• For inboards, check the stuffing box/shaft log. On older boats, it should drip about once every minute; on newer boats with dripless shaft logs, it should be dry.
• When the boat is out of the water, shake the prop shaft at the strut to make sure it’s tight. Inspect the prop at the same time. If it’s dinged, remove it and have a prop shop refurbish it.
• Check the operation of all bilge pumps and float switches periodically.
• There are two schools of thought regarding raw-water impellers. One points to the fact that impellers are difficult to install correctly and that many water-pump failures stem from improper installations. This school’s conclusion is that if no problem is apparent, you should leave the water pump alone. The other school advocates preventive maintenance, urging annual replacement of impellers as a prophylactic. In truth, impellers often last many years if the raw-water strainer is properly serviced.
Troubleshooting
Every make of engine requires specific troubleshooting methods, but here again some general guidelines can be helpful. The most likely problem with a gasoline engine is with the ignition system, followed by overheating. With a diesel, dirty fuel or fuel starvation is typically the culprit, following by overheating. If you have twin engines—gas or diesel—and both quit at the same time, contaminated fuel (assuming you have not simply run out of fuel!) is the likely cause.
Regardless of what kind of engine you have, the number-one rule of troubleshooting is to do the simplest thing first. When your engine suddenly dies, it’s human nature to think in catastrophic terms, but before you haul out that set of wrenches you’ve never used, look at a few basics. Is the ignition key all the way on? Are the breakers on and untripped? Are the fuel valves and seacocks open? Do you have fuel? Are the fuel valves open? A few minutes examining the basics will often solve the problem, costing you little more than embarrassment.
Another cardinal rule is never to try more than one fix at a time. Your objective is not only to restore normal operation but also to learn the cause of the problem so that it can be avoided in the future. If you try two or more fixes before successfully starting the engine, you will not know which fix made the difference and therefore what the exact nature of the problem was.
OVERHEATING If an engine overheats, check first to see if water is coming out of the exhaust. If it is, your problem is likely internal to the engine—a faulty thermostat perhaps—and you’re unlikely to be able to fix it immediately. If little or no water is coming out of the exhaust (and the raw-water seacock is all the way open), check the strainer. On some inboard boats the strainer is external, but on most it’s internal and probably has a clear housing, so you can see if there is debris inside. (Outboard and sterndrive engines pull their raw water from the lower unit; just tilt it up and examine the intake port on the sides of the drive.) If the strainer is clear, the likely culprit is a faulty raw-water pump—specifically the impeller, which is hard to change underway.
MISFIRING This is the most maddening symptom for a boater because there are so many potential causes. In a gasoline engine, it’s often related to the ignition system, and any of the system components may be at fault. Fuel contaminated by water or (more likely) particulates is another possibility for gasoline engines. Generally speaking, newer electronic gasoline engines are more likely to misfire in response to bad fuel, whereas older, nonelectronic engines are more likely to misfire due to faulty ignition components.
In diesels, misfiring is usually caused by one or more faulty injectors. (Fuel contamination usually results in surging, at least initially.) Determining which injector is the culprit and changing it is a job for a trained mechanic. Unfortunately, there’s not much the average boater can do other than limp home.
SUDDEN LOSS OF POWER AND/OR ENGINE SPEED The cause here can be internal or external. Your propeller may have picked up a line. If you have an outboard or sterndrive engine, stop the engine and trim the drive up and out of the water for inspection. If you have an inboard, you may have to don a mask and fins (necessary items aboard, along with a sharp knife) and take a look.
SURGING Generally, this means fuel starvation due to a clogged fuel filter. If you have an auxiliary filter like a Racor, it’s relatively easy to stop the engine and check it. (Note that particulates will not show up in the clear bowl; you’ll have to remove and examine the filter cartridge on top.) If you don’t have an auxiliary filter, your only option is to remove the fuel filter and try to examine it visually, or just replace it, remembering to prime it correctly. Clear bowls are not allowed in gasoline fuel systems, but you can remove the filter element for examination.
OUTRIGHT STOPPAGE A sudden stoppage not preceded by misfiring or other symptoms is a bad sign. In a gasoline engine, it can be related to an ignition problem. Electronically controlled gas engines have a “limp home” feature designed to preclude outright stoppage. If your electronic engine quits suddenly, it’s probably serious, and there’s little you can do other than look for loose wires—including battery cables. If your engine is not electronic, your search will likely focus on the distributor and its internal parts: the rotor, points, and condenser.
Diesels very rarely quit suddenly; stoppage is almost always preceded by misfiring or surging. If your diesel does quit suddenly, it’s often because an electrical malfunction has closed the fuel solenoid, thus preventing fuel from flowing to the engine. The most likely cause is a tripped circuit breaker or broken connection.
Winterizing an Engine
The following steps apply to all inboard engines unless otherwise noted:
• Drain the water from the raw-water system, including the strainer, pump, and all hoses.
• Make sure the engine coolant offers proper antifreeze protection. Coolant does degrade over time. If you’re unsure, drain the system and refill with new coolant.
• Drain the water heater of fresh water.
• Lubricate all seacocks if possible.
• Fill the fuel tanks to 7/8 ths full to reduce condensation, and add an appropriate fuel stabilizer. Run the engine long enough to fully circulate the treated fuel.
• Start the engine and let it warm. Then shut it down and drain the oil. Fill with fresh oil, replace the oil filters, and run the engine briefly to circulate the oil.
• Change the transmission oil when it’s warm.
• Seal all openings into the engine compartment – the air intakes, exhaust, and fuel-tank vent.
• Remove the batteries if practical and store them in a warm, dry place. Charge them regularly.
• Change the oil in the lower unit of a sterndrive engine and grease any fittings.
• Check the prop(s) for dings. Remove and send it out for refurbishing if necessary.
Recommisioning after Winter Layup
• Do a thorough check for signs of leakage or seepage at engine joints. Check for fluid in the bilges, and if any is found, determine the source.
• If you've removed the battery, bring it up to a full charge and brighten both terminals and both cable ends. Reinstall.
• Reconnect any hoses you disconnected at layup, such as those to the water heater. (If you made a checklist at layup, you can simply reverse the steps at spring launch.)
• Check all fluids, noting the levels and looking for discoloration due to the presence of moisture.
• Check the condition of the engine coolant using an inexpensive coolant tester, available at any auto parts store for under $10.
• Start the engine and let it idle for two minutes. Do not rev the engine.
• With the boat still tied to the dock, put the engine in gear for another two minutes, listening for any unusual sounds.
• After your first trip of the season, check all fluid levels and the bilges for signs of leakage.
How to Change Engine Oil
1. Make sure the oil is warm; it need not be hot. Run the engine if necessary.
2. Remove the drain plug if possible. Most engines require the attachment of a manual or electric pump to vacuum out the oil, as the drain plug is on the bottom of the oil pan and inaccessible.
3. While the oil is draining, remove the oil filter. You will probably need a filter wrench, and you may want to put a plastic bag around the filter to prevent oil from dripping into the bilge. In any case, it’s a good idea to always keep an absorbent pad under each engine to catch any fluid drips and keep them out of the surrounding water. Empty the oil from the filter into the same container that receives your used crankcase oil. Dispose of both properly.
4. Place a light coat of clean oil onto the new filter’s rubber gasket and screw it into place. Handtighten firmly, but do not use a filter wrench.
5. Refill the crankcase with fresh oil to the full mark on the dipstick.
6. Start the engine, run until the oil is warm, and check for leaks. After you shut down the engine and let it sit for a few minutes, check the oil level on the dipstick to make sure it is still at the full mark. Add more oil if necessary.
Outboard Engine Maintenance
There are three main types of outboards, and which one you have will determine what maintenance you should perform:
• Most four-stroke cycle (or more commonly just “four-stroke”) outboards require basically the same maintenance as gasoline inboards, including an annual oil and filter change and a periodic (usually every three years) change of spark plugs. You may also need to change a fuel filter. All four-stroke outboards are electronically fuel injected, so they have no distributor. However, some sophisticated models such as Mercury’s Verado require specialized maintenance more often, which can be performed only by a trained technician. Most four-stroke outboards have at least two lubrication points and one to three sacrificial zinc anodes that need to be monitored and occasionally changed.
• Conventional two-stroke cycle (or just “two-stroke”) outboards have not been manufactured for at least 10 years due to more stringent federal and state emissions regulations. Because they burn a combination of oil and gasoline, they have no separate lubrication system and thus do not require periodic oil changes. Burning this mixture makes their spark plugs more susceptible to fouling than four-stroke engines, so periodic—sometimes more than just once a year—spark plug replacement is important. So is lubrication of key pivot points and zinc maintenance. Finally, older outboards lack the durable paint of today’s engines, so touching up scratches and abrasions is important to prevent corrosion.
• The third outboard engine type is the directinjection outboard, notably the Evinrude E-Tec. It too uses a two-stroke combustion cycle and burns a combination of oil and gasoline, albeit via a much more sophisticated system. Sophisticated electronics and high-pressure direct injection allow it to meet all current emissions regulations. According to Evinrude, these engines need spark plug replacement only every three years or 300 hours. As with other outboards, however, there are other maintenance items that must be performed by the dealer.
When in doubt which procedures you should perform and when, consult your owner’s manual. But regardless of which kind of outboard you own, here are some tasks you can do yourself:
• Flush the engine’s internal passages with fresh water after use in salt water. All modern outboards have sophisticated internal corrosion technologies, but flushing out salty water can’t hurt. Many newer motors have easily accessible flush ports to make this job easier. If you don’t have a port, buy a set of “rabbit ear” muffler-type flexible rubber seals that fit over the water pickups on the lower unit. Attach them, connect a hose to a source of fresh water, and turn it on. Start the engine and let it run for two to three minutes.
• Like inboard engines, outboards have rawwater pumps in their lower units. The same divergence of opinion regarding inboard pumps noted above applies: either replace them annually and risk the chance of failure due to improper installation or wait until you see signs of deterioration (reduced water flow) before servicing them.
• Replace spark plugs as recommended by the manufacturer.
• Change the filter element in the auxiliary water/fuel separator once a year, if so equipped.
• Periodically remove the engine cowling and inspect the engine for leakage or corrosion. Check the integrity of the wiring, especially the spark plug wiring.
• Remove any dirt or salt residue with a damp rag and then wipe down the engine with another rag sprayed with a lightweight oil such as WD-40.
• Check the clamps on the fuel lines.
• Check the fuel primer bulb if so equipped. It should be free of cracks and firm when you squeeze it.
• Drain the oil from the lower unit and refill it. Observe its color; if it’s cloudy, that’s a sign of water intrusion and a failed propeller shaft seal.
• Install new sacrificial anodes on the lower unit once a year or as needed.
• Inspect the seals at the prop shaft, especially looking for monofilament line wrapped around the shaft. Look for signs of leaking oil.
• Look for bent or damaged propeller blades. If you see any, send the prop out for refurbishing.
• For winter layover, change the oil in the lower unit and grease any fittings.
• For winter layover, remove spark plugs and spray fogging oil into each cylinder of a twostroke outboard. Replace the spark plugs.
• If you have a removable gas tank, remove it from the boat and store it in a warm, wellventilated place for the winter, or drain it.
Figure 21-15 A cutaway view of a 200-hp, fourcylinder, four-stroke outboard motor with electronic fuel injection. This engine can top out at 6,400 rpm.