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How Often Should Boat Engine Oil Be Changed? – Answered

Written by Anthony Roberts / Fact checked by Jonathan Larson

how often should boat engine oil be changed

The engine is the most vital part of a boat as no movement can be done without it. That’s why every responsible boat owner takes care of it. How often should boat engine oil be changed? This question is one way of responding to this concern.

The marine oil change should be done every 100 hours. Otherwise, make sure to change it at least once every year. It’s the common recommendation of most manufacturers. Still, it’s safe to check your user manual for specifications when you change boat oil.

How Often to Change Your Boat Engine Oil?


Even though the most recommended schedule for changing engine oil is after 100 hours, it doesn’t apply to all boat engines.

Take the owner’s manual as a reference to get the exact information about this. You may also contact your dealer or the engine manufacturer. To play safe, you may change it at the end of each

season or before and after storage.

  • Types of engines

A new engine – There’s a break-in phase for the new engine and it’s the time that you need to change the oil in a diesel engine after its first 20 hours of use. Then, you can do it every 100-hour or yearly.

An old engine – The 100-hour pattern is observed among old engines when you change the oil in your boat’s engine. Bear in mind that it’s a vital process as the engine ages as well as those engines that are not used frequently.

Fresh oil extends the life and service of boat engines. Based on this fact, it’s not a smart move to change the oil in a marine diesel engine every other year.

Here are more tips on how to change the oil based on the engine type.

Type of engine Ideal oil change interval
4-stroke 100 hours
2-stroke add oil often (no need to change oil)
Diesel 50 to 200 hours
Extensively used 50 hours
New one 20 hours (very first change oil) and 100 hours will follow

In a four-stroke engine for utility and trolling, the conventional oil should be changed after 50 to 100 hours. This instruction applies to the need to change the oil in Yamaha 4-stroke outboard.

However, 5.7 Mercruiser oil change should be done in 100 hours or once a year. Boaters would usually have this process during winterization. Some prefer to use synthetic oil for this inboard boat motor.

Conventional oil and synthetic oil have been mentioned. Hence, you may wonder about the right one for your engine. In an outboard oil change, synthetic oil is the better option.

Synthetic oil is more commendable than conventional one, specifically with boat engines that have high horsepower. Cenex, a petroleum company, stated that synthetic oil causes the engine to run quieter, smoother, cooler, and with less smoke.

Changing the oil in Mercury 4-stroke outboard motor is not a problem as there’s specific oil for it. The good news is that Mercury Marine approves synthetic oil for all its engines.

However, the EC-W rating should be used in 4.3 Mercruiser inboard boat motors. The motor oil for inboard marine engines, just like the outboard and sterndrive, is ideally the synthetic type. But just take note of the ratings if they’re required.

  • Recommended oil change intervals

Engines don’t have similar hour meters as well. For instance, 50 hours of operation at a high load is different from the same hours at a light load.

The type of engine oil that you use has something to do with it too. Using quality oil that meets the specification of your engine can extend the interval.

To avoid making mistakes, you have to make sure that you get updated information from your engine’s manufacturer. You may contact the support team for confirmation.

Just like the 250-hour interval of Caterpillar that created the S.O.S. monitoring program to make this possible. The company also recommends a specific oil for it. It’s quite impressive but there are some limiting factors.

How Important is Changing the Oil on Your Boat’s Engine?


  • Fuel economy

The cleanliness and proper lubrication of the boat engine are maintained when you regularly change the oil. With these factors, friction among engine parts is eliminated in exchange for better gas mileage.

  • Keeps engine clean

The accumulation of dirt, dust, and metal particles is inevitable within the engine. But these unwanted things can be removed when you change the engine oil as scheduled.

Once they’re disposed of, you don’t have to worry about damaging your engine. Also, the oil won’t turn into slush if you change the oil on time.

  • To cool down

Oil lubricates the engine so there’s less friction on the engine parts. When the friction is minimized, it means that the heat lowers at the same time. Lubrication and coolness go hand in hand to maintain the engine’s good condition.

  • Engine protection

In terms of operation, marine 4-stroke engines are cooler than the 4-stroke automotive engine. However, it’s not always positive as the present moisture can combine with contamination.

When it occurs, the oil turns into acidic oil that sits down at the bottom part of the engine. It can be avoided if you change the engine oil on time. Don’t ignore this as acidic oil can easily cause rust that leads to serious problems and expensive repairs.

  • Improves engine performance

Oil loses its viscosity when it breaks down and you won’t like it as slush will also form. The oil will fail to reach its destination so it compels the engine to work harder in putting the oil on the move.

As the engine exerts too much effort in lubricating its parts, it hampers reaching its optimal performance. There’s also a reduction in gas mileage. All of these will likely happen when you neglect the necessary change of oil.

  • Prolongs engine’s lifespan

Changing the oil on time provides the necessary lubrication to the engine. The consistency of its great performance can prolong its lifespan.

When Should You Change the Oil in Your Boat?

You should change the oil in your boat before putting it in storage rather than having it after. Harmful contaminants form when the engine is idle. Moreover, it’s also essential to change the lower unit oil of outboard engines and sterndrive in 100 hours or annually.

How to Change Your Boat Engine’s Oil?


Before knowing the proper steps in changing your boat engine’s oil, you have to prepare these things first.

  • Oil pan
  • Oil change pump extractor or inboard boat oil change pump
  • Oil filter wrench
  • Pieces of rags

There are two ways you can change the oil in your boat. Firstly, you can oil change kit for boats and secondly, through an extractor pump. I like the kit from Fox Trot.

Here are the steps to follow:

  • Begin with running your engine for some minutes to suspend contaminants and lower the oil’s viscosity.
  • Turn off the engine before changing the filter and oil.
  • You have to prepare in advance for collecting the sump and filter to avoid spilling. It also makes disposal easy and convenient.
  • Rub some oil on the filter’s gasket so it can sit well.
  • Restart your boat engine for 60 seconds for the oil to circulate. At this point, you have to check for any leaks.

Some boaters choose the pump to get into the engine’s bottom. When you use this tool, you can follow the same steps above but don’t forget to detach the oil fill cup as it’s not needed when using the pump.



How long does oil last in a boat?

Based on the instructions of most engine manufacturers, oil lasts for 50 to 100 hours in a boat. It’s the standard period but some engines require oil change in 200 hours or more.

What happens if I skip an oil change?

If you’re lucky, nothing bad will happen if you skip an oil change. But wear and slush are the outcomes of this negligence. They’re not noticeable at first but the engine is in the danger zone.

When you skip an oil change and you don’t know the present condition of your engine, better take it to the shop. Some tests can be done to identify any damages together with the solution.

DIY vs Taking it to the shop

Not only mechanically inclined individuals can change boat motor oil. Following an instructional video regarding this matter is no sweat. As long as you have the right tools, you can wrap it up in an hour or less. It’s not only easy but you can save money.

How much does changing the oil in a boat cost?

DIY changing the oil in a boat with a single engine costs around $50 to $75. The price depends on the necessary oil filter and the kind of oil. There’s a big increase in the amount which can be up to $300 when you let a professional do it for you.


So, how often should boat engine oil be changed? According to most boat engine manufacturers, changing engine oil should be in 50 to 200 hours. As you can see, there are variations as there are different makes and models. Always refer to the user’s manual for this information.

Quality oil and changing the oil before storage or winterization also make a difference in the interval. Synthetic oil is better than conventional oil but it’s best to stick with the recommendation of your engine’s manufacturer.

Read more: How often should I check the engine oil level?

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