[C320-list] Yanmar 3GM30F - Synthetic - why not

[Pat Ireland]

All

It's about time to change oil and I suspect that synthetic oil should be a
better oil for diesels that standard petroleum oil.  But the manual
recommends not to use synthetic oil.  Does anyone know why synthetic oil
is not recommended for a yanmar 3GM30F?

In looking for data, I found this quote on a web search.   It was in a
thread about cold starting a Yanmar 2GM20.

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After receiving numerous different answers from Yanmars USA tech support
(mostly IMHO run by local distributors who are selling *Yanmar*
non-synthetic
oil), I decided to write directly to Yanmar in Japan about the use of
synthetic
oil ...... the following is the answer I received.
Mr. Guthrie,
Your Yanmar pleasure boat engine should be broken in before using the
sythetic oil. As long as you have at least 50 hours on the engine and it
has be used at all RPMs, then synthetic oil is OK to use. Please continue
to change it at the recommended interval for your engine as specified in
the operator's handbook. You can expect slightly increased oil consumption
and posibly a drip or two under the engine. Synthetic oil tends to find
its way past gaskets and seals a little easier than petroleum based
products. Depending on temperature, you can also use a petroleum based
10-30 or even a 5-20 if it is cold enough. Just be sure to use a premium
grade oil.

Regards,
Earl Helmer
Director, Service Warranty and Engineering

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Anyone have info that would dispute this information?

Pat Ireland, Cherie, 801