“An ounce of prevention is worth a pound of cure.” When it comes to diesel engine maintenance, unless you are a diesel mechanic, the only part of that equation you can manage yourself is prevention. As the owner or operator of a diesel-powered vessel, regular checks and maintenance are your most powerful tool to prevent costly repairs or disastrous engine malfunctions during a voyage. Small issues or overlooked service requirements can quickly snowball into catastrophic damage that will far exceed what you can handle on your own. Staying on top of regular engine checks can help you identify issues early and schedule repairs at a time that suits you.
If you’re looking to DIY any part of your engine maintenance, you probably don’t own a commercial shipping vessel, and if you own a commercial shipping vessel, you ideally have a diesel engine mechanic on board or on call. Regardless of the resources you have available, there are some basic guidelines any marine vessel operator can follow to promote engine longevity and efficiency.
We’ve compiled this guide with a focus on marine engines based on the knowledge and experience of our team here at Diesel Dash. These tips, tricks, and best practices can serve as a reference to help you make the most of your investment and enjoy smooth sailing.
Depending on the size and type of vessel, your engine could take a variety of forms.
To start off, you should confirm that your boat even uses diesel, as vessels under 45 feet may use gasoline engines. There are plenty of resources available online for advice and assistance with marine gasoline engines, but for obvious reasons, Diesel Dash probably shouldn’t be your go-to. Consult your owner’s manual to verify the type of engine your boat is equipped with.
Some vessels such as yachts, motor boats, or large commercial ships use diesel engines as their primary propulsion system. Others, like sailboats, may employ a diesel engine only as backup propulsion in case of windless days. Diesel engines are also popular choices for generating auxiliary power for electricity and other functions on board large vessels. A diesel engine serving in this capacity is called a marine genset.
Depending on the function of the auxiliary engine, it may get more or less use than a primary engine, which can affect longevity. However, an engine that is used infrequently can present its own challenges, such as fuel spoilage, belt brittleness, or rust formation.
While outboard motors are mounted to the rear of the hull, inboard motors are integrated into the bottom of the boat. While there are many differences between the two, the main distinction when it comes to maintenance is ease of access. The inboard motor has to be accessed via a hatch, and the engine cannot be removed easily. An outboard motor can be easily detached from the back of the boat for servicing, cleaning, storage, or replacement. In terms of serviceability, outboard engines are typically preferable, but both require the same basic maintenance tasks.
For larger boats, yachts, and ships (40+ feet), the engine is typically housed in a dedicated engine room.
Marine diesel engines are, at the end of the day, a diesel system like any other, and so the fundamental mechanism and maintenance needs are the same. However, there are also unique considerations to bear in mind that won’t be addressed in maintenance guides for semi-trucks, generators, or any other kind of diesel engine.
Some things to keep in mind when consulting guides focused on general diesel maintenance:
Because of their high-moisture environment, marine diesel engines come equipped with an additional line of protection for their fuel system. Along with the fuel filter, a fuel-water separator acts as a second line of defense to ensure the fuel is completely free of water particles.
While diesel engines in road vehicles rely on airflow through a radiator to keep the engine cool, marine systems use water to perform the same heat exchange task. Most marine systems have a closed fresh water loop that circulates water and coolant through the engine system, carrying away the heat. In turn, the raw water system pumps in water from the body of water the boat is sailing in—whether seawater or freshwater—runs it alongside the fresh water system to transfer the heat from the coolant to the raw water, and then expels it from the engine. The raw water pump and fresh water pump keep the systems flowing, and the raw water intake has its own filter—sometimes called a sea strainer or seawater strainer—to prevent debris from entering the cooling system.
So what are the basic maintenance requirements of a diesel engine? As you may know, diesel engines do not operate in the same way that a gas engine does in a car. Not only is the fuel itself different, but diesel engines generate power by compressing the fuel with oxygen-rich air until it combusts, while gas engines use a spark plug to ignite the fuel. Because of this, diesel engines tend to be built more robustly than gas engines, and thus often have longer lifespans.
However, diesel engines have unique maintenance needs. If care is taken to ensure these needs are met, your boat’s diesel engine may very well outlive you. Listed below are some of the most important maintenance tasks for all diesel systems. Though gas engines also have some of these parts, they are much more important in diesel engines.
Because diesel combustion requires the introduction of clean and oxygen-rich air, air filters are one of the most important parts of a diesel system. These filters prevent particles and water vapor from entering the finely-tuned environment of the engine and causing problems with lubrication, combustion, and more.
Similarly, clean fuel is key to smooth diesel engine operation, as diesel fuel does more than just combust: it also serves as a lubricant and coolant within the high-pressure and high-heat environment of the combustion chamber. The introduction of any contaminant, especially water, can be disastrous for the engine. Diesel fuel filters are critical to maintaining a healthy engine and should be replaced during oil changes.
Just like a gas engine, oil is critical to maintain lubrication across a diesel engine system. And just like air and fuel in a diesel system, the oil used must be kept clean and pure to prevent contamination of the combustion system.
When checking your engine’s oil level with the dipstick, visually inspect the oil to check the quality and purity:
Normal oil is amber to black in color. Perform an oil and filter change at the interval recommended by the manufacturer.
This usually means that there’s fuel in the oil; investigate further and perform an oil and filter change ASAP.
Thick, black oil could mean that the oil is contaminated or forming a sludge investigate further and perform an oil and filter change ASAP.
This usually means that there’s water in the oil; investigate further and perform an oil and filter change ASAP.
A gritty texture indicates a buildup of sludge or contamination investigate further and perform an oil and filter change ASAP.
If there is an odor of diesel in the oil, this also indicates contamination and a possible leak, both in the oil system and the fuel system; investigate further and perform an oil and filter change ASAP.
For all diesel engines, fuel conditioner is an additive that can help prevent fuel spoilage if the engine sits unused for more than a month.
WOBBLES is an acronym that covers the most important pre-departure checks to complete every time you take your vessel out:
After starting the engine:
Other things to check before departure:
Consult your engine’s service manual for any other checks recommended by the manufacturer.
While the list above covers the most essential tasks to complete for the start of a voyage, the following checklist contains a much more comprehensive list of maintenance checks to perform. The frequency of these tasks varies depending on manufacturer recommendations. Refer to your engine’s service manual for maintenance intervals recommended by the manufacturer and see our Maintenance Schedule below for an example of a typical schedule.
Check the following items and record them in a maintenance log:
Exhaust gases from marine engines should be clear. Any color in the smoke is a sign of potential trouble.
After starting the engine, observe the exhaust gases and look for the following:
Following the manufacturer’s maintenance schedule is the best way to avoid unexpected breakdowns. Refer to your owner’s manual for the recommended service intervals for your marine diesel motor or genset. When in doubt, consult a professional marine diesel mechanic.
Here’s a common maintenance schedule for boats with a marine diesel engine. Use this schedule only for reference.
Marine diesel engines are the backbone of the shipping industry. While the modern diesel engine is complex, the basics of owner maintenance are the same as they have always been. Experienced mechanics will tell you that your diesel engine needs four essential things for a long life: clean oil, quality fuel, fresh coolant, and plenty of clean air. For best practice, changing the lube oil, fuel, and air filters at regular intervals does not allow minor issues to become major problems.
It's no secret that routine maintenance on your marine diesel engine will lead to years of reliable service. Besides, who wants to be stranded at sea and then have to call a mechanic or towboat because a simple maintenance task was overlooked? This outcome can be embarrassing, dangerous, and very expensive.
If you’re looking for parts to maintain your marine diesel engine, look no further than our team of diesel parts experts at Diesel Dash! We have a wide range of available parts from Volvo Penta, MTU, DEUTZ, and other top manufacturers that you can order online and have sent right to your door with same-day shipping! We also offer store pickup from our network of locations.
Shop Diesel Dash online or call 833-DSL-DASH for products at a great price.