When we bought our new boat with a new Yanmar
4JH2E I hired a mechanic
from the local Yanmar
dealer who dealt primarily with commercial fishing
He told me that the commercial
Yanmars would easily run 10,000 hours because the commercial owners put them at 70% - 80% power and ran them like that for days at a time (it is a LONG way from Tacoma WA to SE Alaska). They kept them hot and revving.
He said they had serviced lots of glazed and failed Yanmars in sailboats - all failed because, as dozens others have said, Yanmar is a high RPM engine
. He said it is mandatory to run at 3000 RPM
(the 4JH2E) for five minutes every 5 hours or more often. He also said it is critical to run the engine
at 3000 RPM for 10 seconds after docking
- then let is slow to idle for a couple seconds and shut it off.
And... if you start the engine - get it all the way up to FULL operating temperatures before shutting it down. Not reaching full temp (190 F) will not "cook" the acids and water
out of the oil
and will lead to early internal corrosion
He told us to set our Maxprop so we could comfortably run the engine at 2600 - 2750 RPM forever. Our Max RPM is 3200 for an hour and 3400 for five minutes (I think) and he wanted the engine to consistently run in the 70% (~2400) to 85% (2850) range under normal cruising.
And - he said the worst thing a Yanmar owner can do is charge a 12V battery
bank with a 135 amp alternator
- it puts less than 3 HP load on the engine and will quickly glaze it - thus our huge solar
We've followed his advice and have 2850 great hours on the engine.
PS - while testing the injectors at the dock
, in neutral, he had the engine running above 4000 RPM - don't know how far 'cause the tack stops at 4000. I picked up my feet to avoid the flying pistons and rods but he assured me no Yanmar has ever blown due to high RPM.