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Old 05-21-2013
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Runaway diesel

Harborless's problems with a "runaway diesel" is so odd that I really want to know more. How can this happen when the Governor sets the max amount of fuel unless the governor isnt working? Bristol suggested that overfilled oil was allowing oil to be burned instead leading to runaway. Yes, I can imagine an engine continuuing to run on oil but to run away? I woulda thought that in order to run fast that good properties would be necessary and with just the oil, it isnt being injected right.
I've always found that REALLY understanding symptoms solves 90% of problems so we have to get a solid handle on them.
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Old 05-21-2013
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Re: Runaway diesel

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.
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Old 05-21-2013
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Re: Runaway diesel

Quote:
Originally Posted by Frogwatch View Post
Harborless's problems with a "runaway diesel" is so odd that I really want to know more. How can this happen when the Governor sets the max amount of fuel unless the governor isnt working? Bristol suggested that overfilled oil was allowing oil to be burned instead leading to runaway. Yes, I can imagine an engine continuuing to run on oil but to run away? I woulda thought that in order to run fast that good properties would be necessary and with just the oil, it isnt being injected right.
I've always found that REALLY understanding symptoms solves 90% of problems so we have to get a solid handle on them.
Never had a runaway myself. If it is not burning diesel fuel it is burning crankcase oil or oil vapors. Too much blow by vapors accumulating and condensing is a possibility, as is overfilling the crankcase.


http://www.myturbodiesel.com/1000q/s...ine-how-to.htm

Paul T
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Re: Runaway diesel

Using the decompression lever while the engine is running sounds like a very bad idea.
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Re: Runaway diesel

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Originally Posted by charlottea View Post
Using the decompression lever while the engine is running sounds like a very bad idea.
Yeah, the manual for my BMW D7 says very specifically to NEVER use the decompression lever for stopping the engine.
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Old 05-21-2013
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Re: Runaway diesel

That engine in the vid was freaking scary!
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Re: Runaway diesel

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Originally Posted by Rhys05 View Post
Yeah, the manual for my BMW D7 says very specifically to NEVER use the decompression lever for stopping the engine.
Does that manual specifically say how to stop a run away condition?
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Re: Runaway diesel

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Originally Posted by chucklesR View Post
Does that manual specifically say how to stop a run away condition?
It does not (and don't think that I'm questioning your judgement), but I would probably use the "rag in the intake" trick if it came down to it. The decompression lever on my engine is one of the "automatic" variety so that it can be set and then the engine cranked over by hand while the lever clocks around a set number of times before re-engaging compression for the engine to start. Could be that that type of compression lever is a no-no to ever use to stop the engine, but other types are okay?
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Re: Runaway diesel

I get ya Ryhs, and my number 1 is the air intake too.
Some diesels don't have the air intake where you can get to it with a rag, but the lever is right there on top.
I'm not a mechanic and don't have enough knowledge about different types of decompression methods, I just know it WILL shut the engine off as opposed to spraying parts of it and the transmission all over the boat.
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Re: Runaway diesel

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Originally Posted by chucklesR View Post
I get ya Ryhs, and my number 1 is the air intake too.
Some diesels don't have the air intake where you can get to it with a rag, but the lever is right there on top.
I'm not a mechanic and don't have enough knowledge about different types of decompression methods, I just know it WILL shut the engine off as opposed to spraying parts of it and the transmission all over the boat.
Yeah, both are easy to get to on my engine:

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