Yanmar 18 WTF

[Deadline]

I was motoring my H320 on the York River when the Yanmar 18 suddenly ran away, not in gear but revving quickly toward 3,000. Gray smoke bellowed out the exhaust. Pulling the choke barely killed the engine. I went below and it wasn’t overheated. I was reluctant to restart, so we got towed. Next day it started up after some hesitation and has run well since then. Here’s what the Yanmar and other people surmised. I’m curious if anyone else has suffered this surprise. Thanks
• A rag snagged the prop and it momentarily seized up.
• A plastic bag covered the raw water intake, then fell away.
• It was overfilled with oil and finally blew some out.
• Miniscule trash got into the fuel injector, causing a surge.
• A change from Cetane to another additive caused reaction.

 

[Ken13559]

Injector valve momentary stuck open could be a possibility.

 

[kloudie1]

Need clarificatiion.... Ran away but not in gear... had you just shifted into neutral? Did it start to run away before shifting into neutral?
If running away just as you shifted out of gear, probably a sticky governor or sticky fuel rack in the injection pump. If running away as you motored in gear, then the motor is getting "un-governed" fuel. could be that the crankcase breather burped a bunch of oil into the intake manifold and the engine was running on oil until it cleared out.

 

[Deadline]

Response

No, I hadn't shifted gears and wasn't in neutral. It just went kaplooey. For what it's worth, I was doing 2400 rpm instead of usual 2800 simply because I was going slowly in a cruising motif. Perhaps there was a buildup due to that.

 

[jtm]

there's no "kaplooey" in dieisel mechanics!

I'm with kludie on this one

 

[rufus1138]

+1 no such thing as kaplooie, lol, had to be some kind of breather malfunction or a failure of the fuel system. thats the only way a diesel will run away like that and it can definitely happen.