How Often Should Boat Engine Oil Be Changed?

After contacting over 10 different marine engine dealers and reading manuals from 4 different marine engine companies, I’ve concluded this:

You should change your boat’s engine oil every 100 hours or right before you put it in storage (whichever one comes first). However, marine diesel engines can vary between 50-200 hours. If your engine is brand new, it’s recommended to change the oil after its first 20 hours.

Many marine diesel motor makes and models vary widely. So, make sure to contact your diesel engine manufacturer or dealer or check your owner’s manual to find the proper oil change interval for diesel engines. However, if you are unsure, change the oil at the end of every season and you should be fine.

If you use your motor extensively, such as for trolling or utility, it’s generally recommended to change the oil every 50 hours (especially if it’s a 4-stroke or you use conventional oil).

Engine type/usageRecommended oil change intervals
4-stroke gas100 hours
2-stroke gasNo need to change oil (just add oil often)
Diesel50-200 hours
Extensively used gas engines50 hours
Brand new engine20 hours (for one interval, then 100 hours)

When should you replace the oil in your boat?

You should always change your boat’s engine oil before putting it away for storage and not after storing it. This is because oil accumulates harmful contaminants during engine operation that damages your engine over time when left in storage.

To make sure your boat isn’t basking in these harmful contaminants in storage, always put new (clean) oil in before storing your boat. This will extend your motor’s life up to 500 hours.

This is assuming a gas motor (diesel motors can last up to 5,000 hours)

You should also change your gear lube and fuel filters every 100 hours or at the end of your boating season. This can be done by yourself for pretty cheap, or you can hire someone to do it for you.

What kind of oil should you use for a boat engine?

The best type of oil for your specific engine depends on the type, make, and model of engine you have. Each manufacturer gives a recommended oil to use for each motor they have listed either online or in the owner’s manual.

However, pretty much all oil types designed for your motor type (e.g., 4-stroke outboard oil) will work fine, but to ensure you keep a healthy engine, always use the oil that your manufacturer recommends.

Below is a list of the recommended marine motor oil for the different engine makes and models (the links go to the product on Amazon). The list is in order by popular brands.

Engine TypeRecommended Oil
Mercury 4-stroke outboard motorsMercury 4-Stroke F-CW 10W-30
Mercury 4-stroke inboard and sterndrive motorsMercury Synthetic Blend 4-Stroke (25W-40)
Mercury Verado motorsMercury Synthetic Blend 4-Stroke (25W-40)
Mercury 2-stroke outboard motors (low/mid horsepower)Mercury Premium 2-Cycle Outboard Oil for Low to Mid-Horsepower Outboards
Mercury 2-stroke outboard motors (high horsepower)Mercury Premium Plus Two-Stroke High-Horsepower Outboard Oil
Mercury Optimax and DFI motorsMercury OptiMax/DFI 2-Stroke Outboard Oil
Mercury MerCruiser D-Tronic (diesel)Mercury Diesel (15W-40) Engine Oil
Yamaha 4-stroke outboard motorsYamalube 4M FC-W (10W-30)
Yamaha High-Performance 4-stroke (such as V MAX SHO)Yamalube 4M FC-W (5W-30) Full-Synthetic
Large Yamaha 4-stroke outboard motors In Warm ClimatesYamalube 4M FC-W (20W-40)
Yamaha 2-stroke outboard motorsYamalube 2M TC-W3
Honda 4-stroke outboard motors (low-mid horsepower)Honda Marine 5W-30M
Honda 4-stroke outboard motors (high horsepower)Honda Marine 10W-30 FC-W
Volvo Penta gasoline motorsVolvo Penta 10W-40 Full Synthetic Gasoline Engine Oil
Volvo Penta diesel motorsVolvo Penta VDS-4.5 Diesel Engine Oil SAE 15W-40

Should you use synthetic or conventional oil?

I recommend always using the type of engine oil that your manufacturer recommends, but that doesn’t mean you have to. Many times there may be a benefit to using different oil, as it may prolong the life of your boat engine.

Synthetic oil is considered a better option than convention, especially with high horsepower marine engines. The petroleum cooperation Cenex says that synthetic oil helps engines run cooler, smoother, quieter, and with less smoke. (source)

The only real downside to synthetic oil is it’s expensive. Many companies charge 2 times more for synthetic oil than conventional oil.

Synthetic oil pros and cons

  • Cause little carbon buildup
  • Extends engine life
  • Make engines run smoother
  • Less smoke
  • Less noise
  • Longer oil change intervals
  • Cost 2 times more than conventional oil

Many old motors may not recommend using synthetic oil because synthetic oil wasn’t a thing back then, yet synthetic oil will help those motors run better. So in those cases, it’s okay to use synthetic (or synthetic/conventional blend oil) in old engines.

Synthetic/conventional oil blends are a great way to get some benefits of synthetic oil while also not breaking the bank to pay for it.

How much does it cost to change the oil in a boat?

Depending on how much oil you need, the type of oil, and the type of filter, a DIY boat engine oil change will cost around $50-$100 for one engine. A professional will charge about $150-$300 to change your boat’s engine oil.

The majority of people change their oil themselves. Out of the 10 people I asked, 8 said they changed their oil themselves, and 2 said they did it professionally.

How to change your boat engine’s oil?

Every boat is different, so make sure to read your owner’s manual in order to follow the exact directions you need to change your boat’s motor oil.

Many oil companies will sell oil changing kits with everything you need to change the oil yourself, otherwise, you will have to get all the products necessary yourself. This may include an oil pump (which is over $50). So, many times it may just be best to take your boat to a professional.

However, if you want to change your oil yourself, check out the videos below. One thing these videos don’t point out is to make sure you run your engine for a couple of minutes before changing the oil. This will heat the oil and help smoothen the process.

Outboard engine

Inboard or I/O engine

Other fluids that need to be changed or refilled on your boat

There are 4 different types of fluids in your marine engine that need to be changed or refiled including:

  • Engine oil (change every season)
  • Gear lube and differential fluid (change every season)
  • Coolant and antifreeze (change every 2-4 years)
  • Hydraulics including power steering and power trim (refilled often and changed every 5 years)

Making sure you change your engine fluids when needed will help ensure it lasts its expected lifespan. All of these fluid changes can be done yourself for relatively cheap, or you can get a professional to do them for you. There are plenty of DIY videos out there to help.

Changing your marine oil is just one of the many factors in maintaining your boat. Check out this article to see all the maintenance steps.


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