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Runaway diesel

8K views 49 replies 29 participants last post by  Cap-Couillon 
#1 ·
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.
 
#39 ·
North, it means a diesel that runs and runs and runs on its own - so how can you stop it? Remember, diesels ignite by compression, no spark plug. So opening the ignition circuit to stop the engine doesn't work. The case they're discussing is where there's too much oil in the bottom of the crankcase, so it's coming up the cylinder walls as a nice froth, which combusts and keeps the engine going...faster and faster ...

Since it's got a source of fuel and a source of heat, only way to kill it is to cover the air intake, which they're discussing the ups down ins & outs of doing ...
 
#42 · (Edited)
So a large eastcoast dragger is coming into a crowed port. The oiler, trying to get a head start on shore leave has removed,cleaned and rinsed (with diesel fuel) the air filters .He re installs.Wow. suddenly engine is way past governed RPM. Take her out of gear and probably disintegrate or do a fancy two step in small places. Excessive RPM can be interesting. My best experience was a friends hot chevy . Carb linkage over centered and pressure plate bounced off the pavement , came back up through the radio , dashboard and windshield into the night.Presence of mind (turn off the key) would have helped.
 
#47 ·
We had an old carrydeck crane with a diesel engine that became notorious for not shutting down or overrunning. We installed a ball valve just down stream of the the air filter so we could stop the engine. If your filter housing is threaded to the air intake tube, it would be an easy install, assuming you have room for the valve.
 
#48 · (Edited)
The two scenarios for engine runaways are

1 Pneumatic governor usually the single pipe. I have seen an old Mercedes boat engine with one of these. If the pipe breaks or the diaphragm fails they will runaway. You can pull the stop control and the engine will stop.

2 Any engine where the crankcase breather feeds into the inlet manifold. If there is any significant frothing of the crankcase oil and it passes through whatever trap is fitted you get a runaway. Pull the stop control and the engine will not stop you have to cut off the air supply.

If I got a runaway and could not get to the air inlet to stuff a rag in I would pull the decompressor if my engine had one. What ever damage would be done would be less than the catastrophic failure you get from a runaway. Worth doing a dry run to find if you need to remove something to block the inlet. Perkins diesels often have a filter that I would need to be removed before applying the rag.

While I have never witnessed a runaway that actually resulted in an engine failure that was catastrophic I have taken the breakdown truck to a Commer 2 stroke that had run away and so had the driver. There were bits everywhere and one of the pistons was embedded in a brick wall many yards away.
 
#49 ·
Years ago I had a run away in my Hunter 30 powered with a 12HP Yanmar better suited for rice patties. I over filled the crankcase. Started the engine, things seemed fine and then it started to race even though I pull the fuel lever all the way back

Yeah, I knew what could happen so I quickly put the transmission in gear and let the boat do wide circles until the run away stopped. No damages
 
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