Synthetic oil for Yanmar

[Don Rice]

I have read the archives and have decided to replace my Yanmar 3GM diesel oil with Mobil 1. Is there different grades or weights of synthetics for diesels?The other question I have is if the synthetic can be used in the transmission. I was under the impression that regular diesel should be used there.Your comments appreciated,

 

[Steve Dion]

Just be prepared

Don:Many a sailors swear by synthetics for their Yanmars. One problem that you MAY encounter is that your engine may weep oil from any seals and gaskets.This is not always a problem but can be problematic in an older engine.Personally I have not seen the advantages. You still need to change the oil each year or 100 hrs. They claim a life expency of 10,000 plus with petro based oils.I would think that the engine may start a little easier on synthetic oils when it is cold.I would suggest that you stay with the recommended oil in the tranny.

 

[Gerry Cooper]

Diesel synthetics

I use Shell Rotella T Synthetic 5W-40 and haven't had a problem except what Steve indicated - weeping from some joints. This was for me a simple fix - tighten the nuts.I went through the same exercise that you have and decided a 'diesel' synthetic most closely matched the requirement. The Rotella T is designed for Diesel and Gas engines and may have different additivies (to counter sulphur) than straight gasoline oil.Although I haven't tried it, I can't see what the issue would be in putting a multigrade synthetic oil in your gearbox.

 

[Pete]

for what it is worth

I would NOT use a synthetic oil. Unless Yanmar has changed there recomendation they did NOT recomend using a synthetic oil.IMO you don't need it as you should not be working the engine hard enough to justify it,and would gain little if any benfit.As Steve said you still need to change the oil based on time even if you don't get the hours,so there is no cost savings. If the engine was new maybe then I might use it but my expirence has been bad switching to a synthetic after using non synthetic oil,oil seals and gaskets leaked (had to replace a rear main seal)If you really think you have to use a synthetic oil consider a blend of regular oil and synthetic.Just my thoughts for what they are worth !