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Old 03-04-2020, 11:37   #1
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Long idled Yanmar 3YM30's

I have two Yanmar 3YM30 diesel motors on my catamaran that have set idle for about five years. They worked great the last time run. Due to circumstances (mostly) beyond my control, they have been long neglected. The oil was changed shortly before this shut down. I was looking for advise on prepping the motors properly before attempting to start them.
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Old 03-04-2020, 11:48   #2
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Re: Long idled Yanmar 3YM30's

If it were me, assuming no water in oil or any other obvious problem, I’d remove all the injectors and leaving them out shoot a couple of teaspoons of oil or Marvel Mystery oil into each cylinder.
Purpose of this is to get some oil on the cylinder walls so your not starting them dry.
Then LEAVE THEM OUT and put a towel over the holes where the injectors go, and using the starter spin the motor in 5 to 10 sec intervals with three min or so between spins to allow starter to cool. Even a couple of teaspoons of oil in each cylinder could hydrolock, so it’s important to blow it all out before you replace the injectors. There will be some oil that comes out and of course some fuel unless you have the fuel shut off, off, that’s what the towel is for, so don’t use your Wife’s pretty ones she puts in the guest bathroom.
The purpose of this is to distribute the oil and blow out any excess so you don’t hydrolock, and of course it’s to get oil flowing good though everything before you put any kind of compression load on the motors.
Reinstall the injectors and start her up, and then this is I believe important, do NOT baby them, after a good warm up period run them hard, maybe not WFO for hours but certainly full throttle and high power cruise.
Purpose of this is to ensure that the rings reseat in case there was some light rust on the cylinders, basically your going through break in again.
Obviously while your running it hard keep an eye on oil pressure and water temp if possible and if not listen for the horn at least.
You don’t want to spin the motors more than say 10 sec to keep from overheating the starter, it’s not under much load, but being cautious doesn’t hurt, that’s what the three min cool down period before spins is for too.


Or you could just crank them up, almost certainly they will be OK, the oiling and spinning to distribute oil etc is an abundance of caution.

Oh be darn sure the thru hull is closed first so you don’t Waterlog the engines, and I’d put new water pump impellers in, cause 5 years is a long time, and fishing broken impeller bits out of a heat exchanger is no fun.

Run them for I don’t know say 25 hours and then change the fluids including the coolant.

You may want to get a good look at that fuel too, ULSD doesn’t age as well as the old stuff.
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