What Kind of Oil Goes in My Engine and can I use synthetic Oil?

A common question from diesel engine owners is: “Should I
use a diesel grade engine oil and what specification/grade
to use?”

We can start by eliminating the oil you might use in your
auto engine if it’s a gas engine. There are separate lubrication
oils for gas and diesel engines.

So, yes, you should use a diesel grade oil. How to determine
this?

Take a look at the label on the oil container. You’ll see a service
symbol donut. The top part will read something like this: “API Service CI-4 CH-4,CG-4,CF-4,CF/SL”

The C tells that it is a diesel oil. The designations are more specific. For instance CF-2 a current diesel lube oil
category is for “severe duty, two-stroke engines.” If the oil
has all the designations listed above it can be used in a
variety of diesel engines. Below that you will see the oil’s
viscosity. The bottom half tells if the oil has energy conservation
properties.

The specific categories are determined by the American
Petroleum Institute.

Some engine manuals, such as as older Universal Diesel Service Manuals list grades such as CD. This is an obsolete classification
having been initiated in 1955. All of the current grades
listed above can be used in place of CD oils.

To sum up the answer: yes use a diesel specific oil, use the
grades listed on the API Oil chart to
determine if an oil will work with your engine.

A real life example of a specific oil is Quaker State SAE 15W-40 Universal HDX for Heavy Duty Diesel engines. Torresen Marine uses this oil on many diesel engines.

Also when changing you oil make sure to dispose properly of
used engine oil, i.e. not at your marina or boatyard dumpster.
You should recycle your used oil.

Whether you should use synthetic oil is dependent on your engine and its number of hours. Yanmar reccomends against use of synthetic oil. Should you use synthetic oil in your Yanmar during the warranty period this will void the warranty.

Universal/Westerbeke’s answer is different. They reccomend using conventional oil during the first 100 hours of engine life. After that synthetic oil is acceptable. With the variance from just 2 manufacturers you should check with your engine’s maker before using synthetic.

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