yanmar 3hm35 oil/water mixing

[milagroman]

my 3hm35 starts well, doesn't smoke, and doesnt use oil until this event occurred (hours on engine unknown). I usually motor at 2000 to 2200 rpm but to clean things out a bit I ran it at 3200 rpm and after a few minutes I noticed oil mixed in with the exhaust water. shut the motor down and checked the oil. it was overfilled and appeared to have water (gray/green color). changed the oil and then motored back to the marina (about 4 hours) at 2000 rpm. no oil in exhaust and no water in oil sump when back at marina.

questions: what caused the two to mix...bad head gasket? other gasket/seals? why did it not re- occur at 2000 rpm? safe to keep using the engine? I have not run it again at higher rpm because I am chicken, (lol!) but would like to know more about the cause.

any ideas from those with more knowledge/experience?

[rbk]

Does it have an oil cooler? If not then head gasket is the likely culprit. Before you go tearing into it I would check the torque on all the head bolts change the oil a couple more times to ensure all the water is removed. Personally I would run it up again after checking the head bolts and if it happened again I would replace the head gasket for my own personal assurances.

It may never have an issue again if you don't take the rpm up or it could have a total failure in a few years when you least expect it. I don't know the engine but I would also look into any other sources of water ingress as well like a raw water pump. If you end up pulling the head and it looks good it could also be a cracked gallery but I would suspect you'd have a somewhat regular issue of water in your sump and oil in your exhaust if that were the case. My monies on the head torque.

[milagroman]

no oil cooler. I'll check the torque on the head bolts...that could be it, since it seems weird that the head gasket would leak at 3200 rpm but not 2000. thanks for the reply.