How To Change Boat Engine Oil

Learn the essential steps for drilling into fiberglass on your boat, whether installing equipment or making repairs.

With any maintenance procedure, the easier it is to do, the more likely it is to get done. So rather than put off changing your engine oil or transmission fluid, take a few moments to master the procedure so you’ll stop dreading it in the future. Such tasks are necessary, of course, to keep your systems running, but routine fluid changes can also provide opportunities to spot signs of potential problems, such as wear or contamination, before they can morph into catastrophic failure — and equally catastrophic repair bills.

Engine Oil: Inboard Ant (Four-Stroke) Outboard

Engine manufacturers recommend engine-oil changes after every 100 hours of use, or annually, at a minimum. Diesel engines tend to be harder on oil than gas engines, one of the reasons that many experts recommend changing diesel oil every 50 hours rather than the 100 hours commonly quoted. In addition to your normal oil-changing preparations (purchasing the correct type and amount of oil, gathering the necessary tools), place catch pans and oil-absorbent pads beneath the engine and oil filter before starting. This adds an extra layer of protection to keep accidental spills from reaching the bilge.

Bring the engine up to operating temperature before changing the oil. Warm oil not only drains easier but also holds more contaminants in suspension, meaning that more abrasive gunk and chemical impurities will be removed from the engine when the oil is changed. Unlike on your car, inboard marine-engine installations typically provide little or no access to the oil-pan drain plug or enough space below the engine to place an open container to catch the draining oil. Therefore, most installations will require use of an oil-evacuation system, one that uses a manual or electric pump to transfer oil from the engine into a separate container. Oil-evacuation systems range from portable, manual, or electric vacuum pumps designed to remove oil via the dipstick tube to permanently mounted pumps plumbed directly to the oil-pan drain.

Using a portable extractor pump (via the dipstick hole) is also the preferred method for removing oil from a four-stroke outboard. The drain plug for a four-stoke engine is accessible, but it’s so messy to use, due to its location, that the extractor pump is hands down the better way to go.

Part of your oil-changing routine should be inspecting the old oil once it’s drained. Oil that’s milky in appearance is an indication that water, antifreeze, or fuel is present, which could mean anything from a blown gasket to a cracked block. Rub a little engine oil between your fingers. If it feels abrasive or has a burnt odor, be concerned about bearing wear, although it could also simply mean that the oil hasn’t been changed in a while.

Oil Sampling

Sending an oil sample to a lab for testing is more scientific than a visual inspection, but it’s most useful for tracking issues over the engine’s lifetime rather than for spot-checking. Still, a one-shot oil analysis can show unusual wear and the presence of water, antifreeze, or diesel fuel. Think of it as a blood test for the engine — one that may not predict a heart attack but can indicate a risk factor such as high cholesterol. For more on oil sampling, see “Oil Sample Analysis“.

Engine-oil changes should always include the installation of a new oil filter. Drip-free filter replacement can be challenging, though, so you’ll want to place oil pads or a catch pan beneath the filter before you remove it. Another option is placing a large zip-top bag around the filter during removal. Once the filter is removed, the bag can then be sealed and used to transport the filter, further reducing the chance of spills.

Always contain and dispose of waste oil and fluids properly. Your marina likely has a disposal or recycling program available, but there are other options — many automotive-parts stores maintain a waste-oil recycling station as well. Store waste fluids separately until they can be properly disposed of. Mixing fluids can make recycling impossible and create a veritable Hell’s Broth that’s even more toxic (and difficult) to dispose of.

Once the old oil is drained and the new filter installed, the next step is adding new oil. Using a funnel will make adding oil easier in almost all cases — you can even add a short length of hose to the funnel to assist with those hard-to-reach oil fills. Once the proper amount of oil is added, start the engine and look for leaks, particularly around the oil pan and filter. Top up if needed because the new filter is now filled. Keeping a fresh oil-absorbent pad beneath the engine will aid in spotting leaks both after and between oil changes.

The specific steps for your outboard will be outlined in your manual, but the basic process is: Drain, Change, Replace, Fill.

1. Drain the old. This Suzuki has a drain plug you can access easily. Other models will require an oil extractor that goes through the dipstick.

2. Allow the oil to drain into a catch pan.

3. Change the oil filter. On this engine, part of the cowling needs to come off to get at the oil filter.

4. Remove the old filter carefully to minimize spills.

5. Replace with a new filter. Lube the O-ring at the top with a bit of new oil. Replace the drain plug if you removed it.

6. Add new engine oil. The amount and type are specified in your manual.

7 Tips For Easier Oil Changes

1. Always warm the engine before changing the oil.

2. Use a closed oil-changing system whenever possible. It’s simple to use, reduces the chance of spills, and makes it easier to transport used oil to a recycling facility.

3. When changing your engine’s oil filter, wrap the filter with a thick cloth during removal to avoid burning your hands. Write the date and engine hours on the new filter to serve as a visual reminder of when the next oil change is due.

4. Use oil-absorbent pads and containers to prevent and contain accidental spills.

5. Temporarily disable automatic bilge pumps to prevent oil from accidentally being pumped overboard in the event of a spill.

6. Recycle used oil and filters.

7. Dispose of used absorbent pads and rags properly.

Frank Lanier

Contributing Editor, BoatUS Magazine

About Vessel Vanguard

Vessel Vanguard is a leading marine safety and maintenance management software provider dedicated to revolutionizing the maritime industry. With a commitment to innovation and excellence, Vessel Vanguard delivers cutting-edge solutions to streamline operations and enhance vessel performance and safety.

Latest Industry Insights


Embracing E-Boating Efficiencies

Eyeing an electric boat but not quite ready to take the plunge? Here are some ways ...
Yacht charging and fueling up.

Boat Fuel Systems

At the spring boat shows, as you’re looking at new boat models, ask about the fuel ...

The Future of Boats & Boating

BoatUS Magazine editors predict what recreational vessels — and boating in general — will look like ...
Yacht Navigation Light Inspection

Yacht Navigation Light Inspection

I’ve never understood why so many vessels I inspect as a marine surveyor fail in their ...

View All of Our Industry Insights

Navigate maritime with the latest news, practical how-to guides, insightful analyses and more.

Text and photos © 2020 Steve D’Antonio Marine Consulting, Inc.