The 10 Most Common Diesel Engine Issues and Fixes: Part 1

No matter how new or well cared-for your yacht may be, eventually you’ll encounter one or more of these common diesel-engine issues.

Diesel engine room
Fuel filters need to be checked when a potential fuel problem keeps your diesel engine from starting. Courtesy Lenny Rudow

Modern diesel inboard engines are shockingly reliable, but anything mechanical can and will have problems. And every yacht owner should know about the 10 most common diesel-engine issues and their fixes. Troubleshooting many of these problems with a modern diesel engine will often be as simple as glancing at the error code flashing at the helm, but it’s still important that you know what’s going on with those iron beasts lurking belowdecks. And naturally, there’s a lot of information that needs to be addressed. We’ve broken down our top 10 list into a series, and in part one we’ll take a close look at the first five most common diesel-engine issues.

Marine Diesel Engine Overheating Under Load

When a marine diesel engine is overheating under load but not at idle, there’s a good chance that the cause isn’t the one most commonly related to marine engines overheating: blockage at the raw-water intakes and/or strainers. If that were the problem, the engine would probably be overheating whether it was under load or not. Partial blockage is still a possibility, however, so step one in the troubleshooting process is to check out the intakes and strainers, and clean them if necessary. The next culprits are water pumps, their impellers, and supporting systems such as drive belts. Note that if you check the pump impeller and any pieces or parts are missing, replacing the impeller alone may not completely resolve the issue. You also have to locate and remove the bits and pieces of that old impeller or they may continue to clog up the works.

There are plenty of other potential problems like scaled-up heat exchangers or clogged hoses that you may need to check out. Most, however, will likely cause overheating at all speeds. If your problem is related specifically to operation under load, look at the other issues here and you’ll likely find the fix. If not, it’s time to call a pro.

yacht on the water
Smoke? What smoke? A well-maintained diesel may produce a puff of white smoke on start-up, but after that should be smoke-free. Courtesy Lenny Rudow

How to Clean a Marine Diesel Engine

Diesels like living in a clean environment and leaving them caked in contaminants can cause numerous problems. Cleaning one, however, can be a challenge. Steam cleaning is an excellent option, but requires specific equipment that most of us don’t own. The next best method of cleaning a diesel is to first remove chunks or caked-on grease with a rag, then use biodegradable or citrus-based degreaser to completely clean off the outer surfaces. Difficult spots can be scrubbed with a toothbrush or similar soft-bristle brush to loosen up the crud.

Marine Diesel Engine Starting Problems

When your yacht’s engine won’t turn over, the first step is to ensure that the battery switches are turned on and the throttles are in neutral. Then verify that the batteries have juice. If they do, you more than likely have a bad solenoid or a bad starter.

If the engine cranks fine but won’t start, the cause is probably either fuel or air related. That means the first step is checking and cleaning filters—any and all of them. If there aren’t any problems there, you could be dealing with contaminated fuel.

Diesel engine room
Clean engines in a clean engine room make for happy diesels. Courtesy Lenny Rudow

Marine Diesel Engines White Smoke

White smoke is generally caused by unburned fuel. A bit upon start-up when the engine is cold isn’t abnormal, but it should disappear quickly. If not, there’s a good chance you have an injector problem. Piston ring blow-by, worn valve seats, a blown head gasket, or a cracked cylinder head are also possibilities. In all of these cases, finding a DIY fix isn’t in the cards and bringing in a professional is in order.

Charge Air Cooler Marine Diesel Engine Problems

Problems with the charge air cooler can be tough to notice because they commonly take place slowly over time, but the net result is a general loss of power and efficiency. This can occur because the thin metal fins grow dirty on the air side and/or have scaling on the water side. If fins on the air side are visibly dirty, they can be blasted clean with compressed air or gently sprayed with water (be careful not to use enough pressure to bend the thin metal). But a complete cleaning for either side requires a chemical bath, which should only be attempted by a professional.


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