Keeping the Love with Marine Diesel Engine Repair and Maintenance

The marine diesel engine is a true workhorse, seldom breaking down when it’s properly maintained. When it does experience a breakdown, or the engine isn’t performing as expected, it’s usually due to its owner putting off a boat repair or failing to do regular boat maintenance. Given that diesel engines are more expensive than gasoline engines, and being stranded is never fun, it’s never a good idea to bypass routine maintenance or to put off boat repairs. Doing so will only increase boat maintenance costs or could quite possibly ruin your boating fun for the rest of the boating season.

Here is one of life’s truths: It’s no fun visiting your boat in the boat mechanic’s repair shop or waiting at the marina for the mechanic to arrive.

Not Your Grandpa’s Engine

Back in the day, as the saying goes, neither gas or diesel engines were computer-controlled. Today, the modern marine engine is a high-tech wonder but with the caveat that the basic operation of a diesel engine has remained the same for decades. Marine diesel engines may look similar to gas engines, and some boat owners assume the maintenance requirements are the same. However, there are big differences that influence maintenance needs.

Gas vs Diesel

To understand the differences, it’s good to know some of the things that make the gas and diesel engines different. Diesel engines:

  • Have more torque and horsepower, making them particularly suitable for larger boats over 30-feet
  • Produce much less carbon monoxide in diesel exhaust
  • Are approximately 20% more thermal efficient which equates to using fuel more efficiently (depending on the boat configuration)
  • Run at a slower RPM so consistent wear-and-tear is less
  • Are compression combustion engines

Understanding the basics of how the diesel engine works helps with understanding boat repair and maintenance needs.

Gas engines are spark ignition engines. Fuel is first mixed with air and then injected into cylinders. A piston compresses the fuel-air mixture, and using spark plugs for ignition, the fuel is ignited. The fuel mixture explodes and pushes the piston in each cylinder which then begins the crankshaft motion.

A diesel internal compression engine doesn’t need spark plugs and mixes the fuel and air right in the cylinder. Air is drawn into the cylinder, the inlet valve closes and a piston compresses the air by 14-25 times its original volume. The air gets hot from the compression, fuel is injected into the cylinder through a fuel injection valve, which then ignites and explodes. The explosion pushes the piston back out. Piston movement leads to the crankshaft turning. As the piston returns into the cylinder, it pushes the exhaust gases out through an exhaust valve.

Getting Down to Diesel Basics

In a diesel engine, the compression ratio must be much higher than in a gas engine because there’s no ignition system to ignite the air-fuel mixture. The compression ratio for a diesel engine is 15:1 to higher than 20:1 compared to 8:1-10.1: for a gasoline engine. A diesel engine is built to withstand the extreme pressure created by compression.

There’s a four-stroke and two-stroke diesel engine. A two-stroke means the piston goes up and down once per cycle. In a four-stroke engine, the piston moves up and down twice. Diesel engines are high tech today. Many diesel engines are supercharged or turbocharged. A supercharger is an air compressor that increases the density of air supplied to the engine. Each intake cycle gets more oxygen and burns more fuel which increases power. A turbocharger reuses exhaust gas to achieve a higher density of the intake air.

Though the marine diesel and marine gas engines have a lot of sophisticated technology today, the marine diesel engine remains a true workhorse. It’s built to be stronger, last longer and perform under strenuous conditions – like propelling your boat through choppy waters with resisting wind. The key is to perform routine marine diesel maintenance, and make repairs as needed.

All Choked Up

“Oh no! The engine is choking.” How many times does a boat owner say that over the lifecycle of the engine?

It could be dirt or water that’s gotten into the diesel fuel injectors. These types of events happen, and some take place due to lack of maintenance. The following are just some of the common problems that can happen with a marine diesel engine:

  • Air filter is clogged so not enough air intake, leading to loss of power
  • Air lines develop a leak
  • Fuel system experiences sludge build-up
  • Cooling system has a damaged water suction impeller, causing overheating
  • Cooling system has a clogged discharge port, causing overheating
  • Engine gaskets fail
  • Oil line is not maintained, and the correct amount of oil is not reaching the engine components
  • Fuel valve cracks and leaks
  • Engine sensors, gauges and/or alarms fail
  • Fuses blow
  • Belts get loose
  • Mufflers get clogged

Some of these common problems can be avoided with some basic maintenance by the boat owner, like replacing a clogged air filter or tightening loose belts. However, many of these issues are avoided by ensuring you follow a maintenance schedule in which a professional marine diesel mechanic in your city checks for maintenance needs and does necessary boat repairs.

Tips for Maintaining a Diesel Engine

As mentioned, no ignition system or spark plugs are needed on a diesel engine, eliminating a couple of maintenance items compared to the gas engine. But there are still plenty of repair and maintenance needs. Whether or not you can perform some of the maintenance yourself, or should let a marine diesel mechanic do the work, depends on your familiarity with all of workings of the engine and whether you have the right tools and equipment. Some engine components and workings cannot be assessed without a computerized system because of the technology involved.

“Thar it blows” - Check the fuel system filters – Diesel fuel injectors will choke when dirt or water is introduced. Even a tiny amount of either can harm the injections, the combustion process and eventually the engine. Water in the fuel can actually blow the heads of injectors. Many engines have two filters – one to trap large particles of dirt and water and another to catch the finer particles the first filter missed. The fuel filters should be changed at least twice a year.

Getting old? - Check the flexible and steel fuel injection lines for leaks or for signs of aging – Leaking fuel lines are dangerous and can lead to boat fires.

Chip off the old block - Check the air cleaner for blockage – A blocked air cleaner will cause the engine to burn more fuel and lose power.

Dead ahead - Check for corrosion – Corrosion in the engine compartment or on any electrical connections should be evaluated as to the source and the components needing replacement. Diesel engines are designed to minimize or resist corrosion, so any indications of corrosion could mean there’s a problem that’s not obvious.

Pressing needs - Conduct a compression test – A compression test is always done when a marine engine lacks power or runs rough. A marine diesel engine mechanic has the appropriate tools and computer equipment/software to check cylinder compression. The test should also be conducted every time you have the engine tuned up for preventive maintenance purposes.

“What’s that you say?” - Listen to your engine – When the sound of the diesel engine changes or a new sound appears, your boat engine is talking to you. For example, a ticking noise can indicate some serious problems like valves that need adjusting or a rod that is knocking. The diesel engine can rattle, knock, tick and make other noises. The key to boat repair is to get the sound evaluated by a professional marine diesel engine mechanic and to get the cause of the noise fixed before it seriously harms the engine.

Cover up! - Check the turbocharger – The turbocharger should turn easily and shouldn’t have any play. It probably has a turbo blanket too that stops heat from spreading and damaging the engine. The blanket can crack, get dirty or end up covered in oil. The blanket should be kept clean or replaced if it gets too soiled.

Tired of sitting - Regularly change the oil – Many boats are only used for a few hours during each outing and outings can be far apart. It’s recommended that the oil be changed after 50 hours of boating time. When dirty oil sits in the engine, it can damage the internal engine surfaces.

Keeping your cool - Conduct cooling system maintenance – The diesel engine cooling system can be damaged in a variety of ways. It could be an electrical short that degrades the coolant or air is leaking into the system, for example. The coolant needs checking during every tune-up, along with ground connections, pressure cap, anodes and hoses. The water pump impeller is easily damaged, so it should be inspected for damage.

Ahoy there! - Visually check for signs of trouble – Regularly check for things like oil or water leaks; sludge or grime buildup in the bilge; and loose hose clamps.

Brrr! - Always winterize the diesel engine – If you live in a climate where you can’t use the boat during the cold weather months, winterizing the diesel engine is crucial to protecting it from damage. If you do regular maintenance, then you know some of the winterizing steps already, like checking the fuel-water separator for water or dirt. Other steps include, but are not limited to:

  • Filling the tank 95% full with diesel gas and adding fuel stabilizer
  • Coating the cylinders with oil
  • Changing the oil and oil filter
  • Winterizing the cooling system
  • Checking the exhaust system for debris
  • Sealing any engine openings that can allow air in (make sure you uncap them in the spring!).

This is the perfect time to make a list of boat repairs that must get done before it’s time to take the boat out again. It’s wise to let a marine diesel engine specialist check out the engine before you head out on the water when boating season starts. Winter weather can easily damage a diesel engine despite taking all precautions.

There are some general guidelines too that you should follow. For example, flush the engine after every use. Also, marine diesel engines are meant to be operated. When they sit for weeks or months (as many do) during the boating season, the engine is not kept oiled and is more susceptible to corrosion. If you have to let your boat sit for long periods of time in between outings, remember to check the oil, warm up the engine to coat the engine parts and look for oil leaks every time you head out.

Getting Trendy in the Marine Diesel Engine Industry

Modern diesels are often equipped with “common rail” engines. These are engines in which all the cylinders are connected to the rail, and the fuel pressure is accumulated and provided through the rail. Its use today reflects advancements in electronics and technology. It has a high pressure pump and a valve block operated by an electronic control system, so maintenance is critical to avoiding expensive boat repairs. The implication is that maintenance should be performed by a marine diesel mechanic because it requires customized tools.

Diesel engines are projected to experience some major tech-based advances, according to Global Market Insights, Inc. (MarketWatch Press Release, June 1, 2020). The advances are to accommodate a market demand for diesel engines that use ecofriendly fuels, are low noise and have low vibration in order to minimize potential environmental damage. While some advances are triggered by the commercial industries (shipping, leisure cruises, ferries, etc.), they always trickle down to the smaller recreational boat engines.

An environmental focus will continue well into the future. This includes reducing emissions, and diesel engines will need to meet increasingly stringent emissions regulations. Manufacturers have already made enormous progress in developing particulate filters and developing clean diesel engine technology that reduces carbon dioxide and nitrogen oxides (NOx) emissions without lowering fuel consumption.

Another focus is reducing maintenance needs or making boat maintenance easier and quicker. One of John Deere’s marine diesel engines has features like a water-cooled exhaust manifold that eliminates external hoses and fittings that can break or leak; remote oil and fuel filter options; and a closed cooling system that eliminates the need for a seawater pump, sea strainer and anodes.

Cummins developed the Pre-Lube QuickEvac which is an engine-mounted pump with off-engine mounted controls. It lubricates the diesel engine before starting it and removes oil from the engine oil pan in 60 seconds. Diesel engine mechanics can help you keep your diesel engine running smoothly and adhere to environmental regulations for oil containment.

You can expect more features like these on diesel engines in the future.

Never Skimp on Boat Maintenance and Boat Repairs

Though there are many steps a boat owner can take to maintain a diesel engine, the reality is that more maintenance steps will require a diesel engine technician who is specifically trained on current model diesel engines or older models that are rebuilt to incorporate new technologies. In many cases, evaluating the diesel engine and performing some maintenance steps requires electronic diagnostic scanners.

It goes without saying that every marine diesel engine of every age needs regular maintenance. It’s mostly a matter of what you can do versus what a mechanic should do.

It’s really not much different than newer car engine maintenance. Remember the iconic picture of the guy getting greasy while fixing his motor in his front yard? Today he’s found sitting in a repair shop waiting area. It’s the same for boat owners, except they are “sitting on the dock of the bay watching the tide roll away” while the diesel mechanic uses his or her expertise! There are expert diesel engine service technicians in every city, so help is never far away.

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