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Old 08-15-2013
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Re: Runaway diesel

Originally Posted by chucklesR View Post
Run away on oil has happened to me once.
I put too much oil in while changing it (boat wasn't level while on the hard), then on my first time out decided to test throttle to max RPM. Frothed it right up. Huge clouds of blue smoke and no throttle control all of a sudden.

The governor doesn't do a thing, it only shuts off/restricts the diesel fuel - so the engine continues to get a full load of 'fuel' from the oil froth.
The fuel shutoff (mechanical and electrical both) does exactly as much good as the governor, none.

Since it's got PLENTY of fuel there and air coming in the engine just does what it is designed to do and runs at full out to use all the fuel coming in, and of course more fuel means higher rpm.

The only way to stop it is to choke air (a rag in the intake) or decompress the engine by tripping the lever on the engine.
You'll need to recognize the condition of run away quick - spinning parts at 4000+ RPM can quickly destroy an engine.

Having had it happen to me just once was enough. I keep a rag zip tied in the the air intake area as well as a zip tie (red) on the decompression lever. It's hard enough to stick your face and hand into a engine compartment with an engine that might be exploding in seconds - doing that and then having to look around for a rag/lever doubly sucks.
if the problem is with the fuel delivery system, as mine seems to have been,maybe, the engine will stop running when all injectors are cracked. my engine is perkins .. they are difficult to cut air.

runaway diesel is also caused by engine using its own lube oil to run and continues to increase rpms until overheat and detonation. this one must cut off air flow or ditch compression so it stops or it will detonate and you can lose boat. this cause is not fixed by cracking injectors, i have been advised.

this is mainly caused by excessive blowby, excessive cylinder wear, ring failure...worn, broken, cracked....
mine so far seems to have been fuel delivery initiated.

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formosa 41 and ericson 35mII
cruising tropical mexico at present, working my way southward

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Last edited by zeehag; 08-15-2013 at 11:41 PM.
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