Maintaining Your Boat’s Diesel Engine

With all the buzz about electronically controlled and high-pressure common-rail diesel engines in boats these days, one of the obvious questions is, can I take care of this engine myself? The answer to that question really depends upon your own skill level as a mechanic and how much work you’re willing to put into maintaining your own equipment. For sure there are certain things on a typical maintenance checklist that might best be left to factory-trained personnel, but that said, even with the high degree of sophistication incorporated into modern engine technology, there are still plenty of maintenance procedures that a handy boat owner can accomplish with great success, not including basic things every owner should check each time the boat is run, including fuel level, oil level, coolant level, belt tightness, and strainer obstruction.

The 370-hp Volvo Penta IPS500 is a modern turbocharged common-rail diesel. In this photo the engine is mated to a pod drive system with twin counter-rotating props. Note that the filters on the port side of the engine are easily accessible for changing. Volvo Penta photo.

Whatever maintenance chores you take on, it’s important to follow your engine manufacturer’s maintenance schedules. Most modern schedules are based either on hours of engine operation or time elapsed since the last maintenance procedure, typically given in months. So, your own usage habits will dictate how often maintenance items need to be dealt with.

The basic areas that need to be dealt with look like this:

Fuel System

Lubrication System

Cooling System

Air Intake and Exhaust Systems

Electrical System

Engine Cylinder Head and Block

Miscellaneous Items/Emission Control System Maintenance

Let’s walk through the important points concerning each of these systems, paying attention to some do’s and don’ts related to whether a particular chore is recommended for the boat owner or for a professional.

Fuel System

After the initial servicing, which is typically recommended after approximately 50 hours of service, fuel-system service items are to be checked and/or replaced at 250-hour intervals or annually. The chief culprits in most fuel problems are water intrusion and often the related problems of contamination and sediment. Here’s the list of service items:

Drain water and sediment from the fuel tank if it is drain-equipped.

Drain water from fuel/water separating fuel filter.

Replace primary and secondary fuel filters.

The topic of marine diesel fuel can be complex, especially since some manufacturers of the newest diesels with emission controls require the use of lubricity additives in the fuel. You will need to find out if this is a requirement for your engine right from the start. Additionally, engine manufacturers are now recommending that fuel injector spray patterns be checked every four or five years or 1,000 hours. In consideration of the extremely high pressures involved, there’s a danger to people in proximity to the injectors while they’re being tested. Also, specialized equipment is needed to properly test the injectors, so this testing procedure will be in the don’t category for most boat owners. Let a trained professional handle it. Further to this, some manufacturers are now recommending replacement of these fuel injectors every 2,000 hours or eight years, whichever comes first.

It’s also important to remember issues of fuel starvation in this service area. Make sure that the fuel filters used are in accordance with the manufacturer’s recommendations regarding micron levels, and check to see whether a fuel lubricity additive is recommended due to the use of low-sulfur fuel.

Oil-changers like the one shown at left are available from most marine supply stores. The 12-volt pump on the reservoir attaches to a boat battery and the thin tube is inserted through the dipstick hole to pull used oil up from the engine sump. The engine should be warmed up first to make it easier for the oil to flow. Doug Logan photo.

Lubrication System

Strictly following engine manufacturer recommendations for engine oil grade and viscosity are is an extremely important maintenance item contributing to long engine life. Cheating here to save a buck is false economy! As for the frequency of oil changes, the numbers vary slightly from one manufacturer to another, but are in the range of the 250-300 hours, or annually. For most recreational boaters, this will typically amount to an oil change with filters each season, and the oil change will be for both the engine and transmission. This as a relatively easy maintenance procedure, so this one ends up in the do column for many owners. One challenge here is probably going to be access to the oil sump drain, which in most cases is not easy unless the manufacturer has installed a plumbed-in remote drain. So, pumping the old oil out through the dipstick tube is the typical method used. Pump-out kits are sold by most marine supply houses and are available in manual suction pump or electrical pump configurations. The best advice here is to warm up the engine and transmission before attempting to pull the fluids up through the suction hose on these pump set-ups. Things will go much more easily with warm and less viscous fluid.

An important tip to remember regarding the oil-change procedure is to make sure the seal for the old oil filter comes off with the filter when you remove it. Lubricate the seal on the new filter before you spin it onto the engine. Also remember that the threads the filter spins back onto are already oil-soaked and the new filter will spin on quite easily. Don’t over-tighten it! Spin it on until the filter seal contacts the engine block and then give it perhaps three-quarters of a turn beyond that point — no more than snug, or hand-tight. Over-tightening will make for a bad day the next time you try to remove the filter! The procedures discussed here are definitely do items for the handy boater.

The intrusion of water into diesel fuel can make a breeding ground for microorganisms and lead to severe fouling, as shown in this blackened Racor filter element. Doug Logan photo.

Cooling System

Next to your engine’s oil, the coolant used is of paramount importance. Understand that engine coolant is much more than merely an antifreeze product. Modern engine coolants are a complex blend of chemicals that help to minimize corrosion, raise boiling points, neutralize engine by-products of combustion, and keep things from freezing. This is another area where following the engine manufacturer’s recommendations for acceptable coolant products is extremely important. Basic service intervals for changing engine coolant will vary now that “long-life” coolant is available, as long as the engine manufacturer allows for their use.

Take heed of the recommendations. This is a lesson I learned the hard way some 40 years ago with one manufacturer recommending a proprietary coolant product that at the time cost about $8 per quart. My inexperienced self decided that $32 per gallon was a total rip-off and I had my customers using a classic Prestone product. That is until we started having engine internal coolant leaks into the engine oil. Turns out that the cylinder liner seals were being attacked by some chemical in the Prestone. That lesson cost me three liner seal replacement jobs on three different engines. That was one of many lessons I’ve learned the hard way. So, besides changing engine coolant based on engine manufacturer’s recommendations, some of the other cooling system items you need to deal with are:

Check for raw water circulation exiting the engine exhaust whenever the engine is running. Note that in some cases this may not occur until the engine reaches operating temperature.

Check coolant level before starting engine each time.

Check and replace the seawater pump impeller every 250 hours, or seasonally.

Replace engine cooling system raw-water (seawater) anodes annually.

Check and clean seawater strainer each time engine is run.

Clean cooling system seawater passages at least every two years or 500 hours.

These procedures fall into the do category for the handy boat owner, with the possible exception of water-passage and heat-exchanger cleaning procedures, which are often done at the end of the boating season when the engine is winterized. Yanmar recommends dealer service for that item every four years or 1,000 hours, whichever comes first.

A new turbocharger has been mounted on this Yanmar diesel. The air filter fitting to the right can be removed to inspect the intake side of the turbo. Doug Logan photo.

Air intake and exhaust system

The procedures here will vary depending on the manufacturer and the equipment installed on your engine. If you don’t have a turbocharger, things will be a bit simpler.

Air filter: Many engines in marine applications simply don’t have or need air filtration, since dust just isn’t much of a factor on the water. However, many engines do have filters, and these need cleaning or replacement at least every year. Many amount to nothing more than a foam element that can be washed out. If there’s a paper element filter, replace as needed based on a visual inspection.

As for the exhaust system, cleaning and/or replacement of the exhaust seawater/mixing elbow at the exhaust riser may be required. Typically, these are made of cast iron and in the saltwater world rust will be a concern. Some manufacturers recommend checking these each season by removing the rubber hose that connects the engine seawater cooling hose to the mixer at the elbow of the exhaust riser and looking for excessive rust. If it appears to be rusty, or the passageway is partially blocked, you should remove the exhaust riser and clean it out thoroughly. Be mindful of the fact that the studs that hold the riser to the engine’s exhaust manifold are also going to be rusty and may need some heat applied to help loosen things up for removal. If you see excessive rust on the mounting bolts and hardware and manifold, this may fall into the don’t category. It may be best to call in a pro to get this part off your engine with a minimum of hassle.

If your engine is equipped with a turbocharger, remove the air intake hose or filter assembly and look down inside the turbocharger inlet. If there is any oil accumulation noticeable, stop! Turbo oil seal leakage is a serious problem that needs to be attended to immediately. The seal keeps the engine oil pressure feed to the turbo rotor bearing lubricated and inside the bearing housing. If that seal reaches the point where its leaking is too severe, there’s a possibility that your engine could go into runaway and actually run on engine oil, with no easy way to stop unless it’s equipped with an emergency shut-off. This whole event can be an engine destroyer! Call in the pros to assess and repair as needed. Again, this is typically a don’t procedure for most boat owners. Some engine manufacturers recommend cleaning the turbocharger annually, but again this is a service your dealer or mechanic should handle.

Make it a habit to pay attention to your boat’s exhaust discharge. There’s often a bit of smoke immediately after startup, but it should disappear quickly. If smoke persists, whether it’s blue, black, or white, you’ll need to investigate.

You don’t have to be a marine electrician to make sure wiring connections are secure and protected. Remember that on boats, corrosion is the enemy, especially in saltwater environments. Ed Sherman photo.

Electrical System

Most electrical system maintenance items are do items for the average boat owner. Some of the items on the list are more or less intuitive. For example, you should confirm that you know what an engine overheat or low oil-pressure alarm sounds like. This is the sort of thing that should be noted every time you start the engine. If your boat is equipped with serviceable batteries (many aren’t today) you should check the electrolyte level at least monthly. Annually you should look over your electrical connections to the engine(s) and make sure that nothing has come loose. Make sure that the insulating boots at positive connectors to the alternator and starter motor are in place. Most maintenance schedules will discuss checking alternator drive belts (V-belts) and adjusting annually. If you have a newer engine with a serpentine drive belt, it should be self-adjusting. Simple vigilance does help prevent most electrical problems on boats, but when in doubt, call in the pros.

Engine Cylinder Head and Block

Beyond a visual check for leakage of fluids, the items in this area are don’t procedures for all but the most experienced and mechanically inclined. Things like torquing cylinder head bolts and valve adjustments require both special equipment and a trained hand on modern engines. A typical frequency for these procedures would be about every 1,000 hours or four years.

Emissions and Miscellaneous Items

Things like fuel and coolant hoses fall into the miscellaneous category. Service schedules will dictate swapping these out every 1,000 hours or four years. This is a do area for average boaters. As for emission-control-related service items like cleaning fuel injectors and checking their spray patterns, injection pump adjustments, turbocharger adjustments, and checking electronic engine control units and sensors, the special tools needed as well as authorized factory training dictate that these are don’t items for the average owner. The good news on this front is that routine maintenance is recommended only every 3,000 hours, which for most boat owners is over a decade of use. However, this is certainly something to consider if you’re looking at a used boat.

Written by: Ed Sherman

Ed Sherman is a regular contributor to boats.com, as well as to Professional Boatbuilder and Cruising World, where he previously was electronics editor. He also is the curriculum director for the American Boat and Yacht Council. Previously, Ed was chairman of the Marine Technology Department at the New England Institute of Technology. Ed’s blog posts appear courtesy of his website, EdsBoatTips.