Join Date: Dec 2004
Thanked 57 Times in 57 Posts
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Re: Runaway diesel
Badly worn valve guides coupled with very hot engine oil that has been diluted with fuel (sticking injectors) (and as a result the oil level is very high and beginning to froth) is a recipe for runaway. The oil will continue to lubricate...after all diesel is "fuel oil" and a good lubricant...but when the level gets high the crank will begin to act like a food mixer and whip the oil/fuel mixture into a froth. If the crankcase can't ventilate properly pressure can build up in the crankcase and accelerate oil accessing the cylinders through worn internal passages.
Check your oil level regularly. Smell the dipstick to see if you can smell diesel fuel in the oil. Rub the oil on the stick between your fingers when you check it (both cold and hot) so you get familiar with the viscosity of good oil and will recognize if it has been diluted.
Check your exhaust for BLUE smoke. From the interwebz (Neptune Products - no affiliation):
"Blue smoke is caused by engine lubricating oil burning. The oil can enter the combustion chamber from several sources including ..
Worn valve guides, or seals
Cylinder &/or piston ring wear
Piston ring sticking
Incorrect grade of oil .. too thin and getting past rings, or valves guides
Fuel dilution of the oil, making it too thin.
Blue smoke is often evident at cold start, which can reflect reduced oil control due to carbon fouling deposits around the piston rings and/or cylinder glaze (which is actually carbon deposited in the machined cylinder crosshatching. These tiny grooves actually hold a film of oil, which in turn completes the seal between the combustion chamber and the oil wetted crankcase).
Blue smoke should not be evident at any stage.
An engine may actually burn oil without the evidence of blue smoke, because good compression burns oil quite cleanly, however, it is not acceptable for any new engine, or engine in good internal condition to burn large amounts of lubricating oil .. with or without blue smoke."
It is a MUCH better idea to block the air intake of an engine to stop runaway than to use decompression levers. Many of us have no remoter operator on the levers and would have to reach over and "hug" that running-away engine to operate them. Perhaps I should install a cable on my decompression levers? H-m-m-m-m...