How To Change The Oil In Yanmar 40hp Diesel Engine

Yanmar 40hp on SV Cadence - Yanmar Diesel Engine for a Sailboat

How do I change the oil in my Yanmar 40hp diesel engine? This was the question I needed answers to, as I knew that changing the oil and oil filters in my Yanmar diesel were essential to avoiding unwanted breakdowns and costs!

I researched the forums, Yanmar Facebook groups, and the Yanmar engine and here is the best advice I found, and followed, about changing the oil in a Yanmar 40hp engine.

About this post: Time to skim, 90 seconds. Time to read, 5 minutes.

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It's easy to change the oil in your sailboat engine like this Yanmar 40hp diesel.

Basic Info About Oil Changes

Engine manufacturers such as Yanmar recommend oil changes every 100 hours, or once a year, whichever comes first. Even if the manual of your engine allows a longer time period before an oil change, most mechanics advise otherwise. Changing the oil can prevent mechanical mishaps and wear and tear.

Boatus.com advises that diesel engines require oil changes every 50 hours because diesel engines are much harder on their lubrication. This is especially true for sailors, who only use their engines for 1 or 2 hours per outing.

How to change the oil in your sailboat - Yanmar 40hp Diesel Engine

How To Change The Oil In A Yanmar Diesel Engine

Yes, there are really two ways to change the oil:

  1. Through the drain plug under the engine.
  2. Pump out through the dipstick.

For most sailboats, it’s impossible to fit a pan under the Yanmar. So the dipstick method is best.

Here’s my first time using the dipstick method (with an inferior tool):

5 Simple Steps

Time needed: 1 hour

5 Steps to Changing the Oil in a Yanmar 40hp Diesel

  1. Run The Engine for a Few Minutes

    This will warm the oil and decrease the viscosity (the thickness). Doing this step will allow you to pump the oil easier. Let the oil drain down to the pan for about 5 minutes after stopping the engine.

  2. Pump Out The Oil

    Use a pump of your choice to pump out the oil via the dipstick. Some pumps will have a hose that goes over the dipstick to create a vacuum. Other pumps will have a hose that goes down through the dipstick valve.

  3. Remove the Oil Filter

    The oil filter should only be hand-tight. But an oil filter wrench can help reach in hard spaces. Important: Be sure the gasket (rubber O ring) comes off with the filter. You don’t want it left behind when you install the new oil filter. It will create a leak!

  4. Oil and Install the New Filter

    Apply fresh oil to the new filter’s O-ring to ensure it doesn’t grab and twist during install. Also, fill the new filter up to half full with fresh oil to reduce the volume of air. Install it hand-tight (3/4 turn past tight).

  5. Fill With Fresh Oil

    Consult the manual to fill with the proper amount of fresh oil. Check the level with the dipstick and ensure you fill to the high side, but not above! Important: Filling above the high side on the dipstick can create frothing and cause problems.

Oil Change Advice from Sailors

After searching the sailor forums, I found these tips worth sharing for changing the oil in our 40hp Yanmar 3JH3BE

It’s easier to add oil than remove. So take it easy when adding fresh oil back into the engine.

Pour about the same amount of oil you took out back in. Once the level is right, run the engine to circulate the new oil. Done. When first adding oil back I aim for the low end of the mark on the dipstick. It’s a lot easier to add a bit more than to have added too much and then have to remove some.

Mike O’Reilly

Of course, you can pay for the first oil change from a Yanmar certified mechanic, and learn by watching.

I still get a Yanmar trained and accredited expert occasionally because they know my engine. As a newbie I think its an excellent idea to pay $100 to have a guy who knows your engine intimately teach you this first time.


And here’s an insight on the filter and not overfilling the oil:

…remember that there is going to be oil in the filter that isn’t going to show up on the dip stick, if you fill the filter with oil first, so you do not want to fill to the full line on the dip stick until after you have run the engine for a few minutes after the change.


And here’s the tutorial I used to guide me through the process. It offers basic, yet valuable advice on oil changes:

Why Is Oil Important?

Diesel engine oil performs three vital functions for your Yanmar engine:

  1. It lubricates internal parts to ensure they function for many thousands of hours.
  2. Engine oil keeps the internal Yanmar temperatures within an appropriate range.
  3. It traps potentially dangerous contaminants such as sulfur and prevents carbon buildup.

We make it a practice to check our diesel engine oil and transmission oil before each trip or day sail in Cadence. A lack of oil can turn a beautiful day on the water into an expensive mistake.

In our last oil change, we used Mobil Delvac 1300. It was used by the previous owner as well. Our engine has 400 hours on it.

Which Oil Do I Use on the Yanmar 40hp?

Diesel engine oil is rated based on performance and viscosity (thickness).

API Rating

API (American Petroleum Institute) oil ratings start with an S or C.

S stands for spark as in a gasoline engine, and C stands for compression such as your sailboat’s diesel engine.

The Petroleum Quality Institute of America offers this graphic to detail API ratings:

Engine oil Specifications for Sailboats - 15w40 vs 10w30 depends on the temperature.
Ambient temperature in ºC

Choosing the Right Viscosity

The number in the oil rating represents the weight of the oil. The higher the number, the thicker the oil.

The W in the oil rating (i.e. 5w-30, 15w-30) represents winter. In other words, the viscosity of the oil changes based on temperature. Colder temperatures (such as in winter) will force the oil to be thinner (e.g. 5w is thinner than 30). Warmer temperatures will create a thicker consistency.

What thickness is right for you?

  • Follow engine manufacturer recommendations
  • If you operate your boat in consistent temperatures, choose a single-weight oil (e.g. SAE 30)
  • If you operate your boat in a wider temperature range, select multi-viscosity oils (e.g. SAE 10W-30). They behave like thin oils in cold weather, making it easier to crank the engine. In high temperatures they work like heavier oils, increasing the level of protection.

Questions and Comments

What questions do you still have about Yanmar oil changes? What did I miss? I’m happy to answer your questions in the comments below.

Also, What tips can you share? What have you discovered? Share in the comments below.





2 responses to “How To Change The Oil In Yanmar 40hp Diesel Engine”

  1. […] maxed out theRPMs on the 40hp Yanmar diesel engine, and the barge laid hard on the […]

  2. Christian Ferree

    How much oil is needed for an oil change?

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