Extend Your Marine Engine Life With These Tips

As every cruiser knows, your engine might not be the heart of your boat, but it’s definitely the lifeline. That’s especially true when the wind dies or you need to punch through a tricky inlet.

With fall haul-out season approaching, it’s a good time to revisit the basics of diesel engine care: clean fuel, proper lubrication and smart layup strategies that help prevent problems offshore or dockside.  

To dig into some of the most common questions sailors have about fuel and oil systems, Cruising World spoke with Bill McDonald, a longtime pro angler and Lucas Oil ambassador whose marine experience extends to fishing and cruising vessels. From stabilizing fuel to catching wear issues early, here’s what he recommends for keeping your engine healthy, whether the boat is on passage or on the hard.

CW: Contaminants in diesel fuel and engine oil are a constant concern aboard cruising boats. What practical steps can sailors take to minimize contamination, and what role can additives play?

BM: Fuel contamination is one of the most common culprits behind engine problems offshore. Regular maintenance—changing fuel filters, draining water separators and keeping tanks full to minimize condensation—is your first line of defense. Additives designed for marine fuel systems can help disperse water, clean injectors and reduce buildup over time. I’ve used Lucas Marine Fuel Treatment for years in both gas and diesel engines. It’s made a noticeable difference in how clean my injectors stay. In the crankcase, oil stabilizers can provide an extra layer of protection by improving lubricity and reducing wear, which is especially useful when cruising far from shore-based repair options.

CW: Marine engines often sit idle for long periods. How can sailors preserve fuel and oil health during layups or long crossings?

BM: Fuel starts degrading the moment it’s stored. Using a stabilizer when you fill your tanks—ideally just before a long idle period—can help prevent oxidation and gumming. Once it’s added, run the engine briefly so the treated fuel circulates fully through the system. The same idea applies to oil stabilizers: Adding them before a layup helps coat internal components and protect against corrosion and dry starts when it’s time to fire up again.

CW: For sailors using ultra-low-sulfur diesel, what’s the risk of reduced lubricity, and how can that be addressed?

BM: ULSD lacks the lubricating properties of older diesel fuels, a characteristic that can lead to premature wear in injectors and pumps. Many cruisers now use upper-cylinder lubricants or fuel conditioners that restore some of that lost protection. They often include detergents too, which can be helpful for keeping older systems clean.

CW: Why is it important to use marine-specific lubricants instead of automotive products?

BM: Marine engines operate under tougher conditions: long hours at high rpm, and exposure to moisture and salt. Marine-grade oils are formulated to resist corrosion and foaming, and to maintain their properties under heavy load. Using automotive oil may not provide the protection your engine needs in these conditions. 

CW: When should sailors consider using oil additives, and what are the signs that it might help?

BM: Additives shouldn’t be used to mask a real issue, but they can help reduce wear, lower operating temperatures and extend engine life, especially in older engines. If your engine feels sluggish, runs rough or is harder to start than usual, it may be worth looking into oil treatment as part of a broader diagnostic and maintenance approach. 

CW: What’s your advice for diagnosing fuel system issues at sea, and how can sailors prepare?

BM: If your engine starts stumbling or loses power, it’s often a fuel problem: clogged filters, moisture or dirty fuel. Prevention is key. Treat fuel consistently, carry spare filters, and know how to change them underway. Having the right tools and basic familiarity with your fuel system goes a long way. 

CW: Some sailors still encounter ethanol-blended gasoline when fueling dinghy outboards or generators. What’s the risk, and how can it be managed? 

BM: Ethanol absorbs water and can lead to corrosion, phase separation, and damage to seals and hoses in small engines. If you can’t avoid ethanol-blended gas, then use a conditioner designed to counteract those effects. It’s a simple step that can prevent a lot of headaches, especially when fueling at unfamiliar docks.

CW: Do you have any advice for boats operating in tropical or high-humidity environments where corrosion is accelerated?

BM: Salt air and humidity are relentless. Rinse thoroughly with fresh water after outings, check electrical terminals for corrosion, and use anti-corrosion sprays where needed. Good airflow in the engine room or lazarette can also help reduce trapped moisture. Regular inspection is the best prevention.

CW: With more cruisers doing their own oil analysis, what should they be looking for? And can additives affect the results?

BM: Watch for signs like elevated wear metals, thinning viscosity or contamination. Additives can help reduce wear particles and maintain viscosity, especially under load. When I started adding Lucas Oil Stabilizer to my maintenance routine, I saw a drop in wear metals on my reports. But if analysis shows recurring problems, that’s your cue to adjust service intervals or investigate further.

CW: How often should fuel and oil systems be treated during extended cruising, and how does usage affect your maintenance schedule?

BM: Your maintenance rhythm should match your usage. Liveaboards and long-range cruisers may need to treat fuel and change oil every few hundred hours; seasonal sailors might only do this once or twice a year. What matters most is consistency and prepping properly before layup. If you’re using additives, follow the recommended ratios and make sure they’re mixed thoroughly and circulated through the system.

Our final takeaway? Marine engine health is about more than just oil changes. A full-system approach includes clean fuel, good airflow, and protection from corrosion and wear. Additives can help extend engine life, but only when they’re used alongside routine maintenance and thoughtful operation. 

It’s work, yes. But when the wind dies, you’ll be glad you put in the time.

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