Sea Foam for dieseling 1968 Cutlass [SOLVED]

Dieseling: I have a 1968 Olds Cutlass. It has been dieseling a lot lately. Can you recommend a fix? Will Sea Foam in the crankcase work to reduce this problem?

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Jim D.
Jim D.
11 months ago

Dieseling is often caused by excessive carbon buildup in the chamber hemispheres that gets hot (like charcoal) and causes the fuel to ignite. Could also have a hot spot on a spark plug. I would keep the tank fuel low and regularly add a can or two of Sea Foam Motor Treatment or High Mileage – the higher concentration will work to soften and clean the varnish/carbon buildup as you run your Cutlass.

Another idea is to treat the upper engine with Sea Foam Spray through the air intake – consider you’re running a whole can over the intake valves and into the chambers in a matter of 5 or so minutes. You can also remove the spark plugs when hot to spray into the chambers and let soak for a few days at a time.

If the dieseling is related to stuck/dirty compression or control rings, Sea Foam in the oil will help clean the rings. Add 1 oz of Sea Foam per quart of oil 100-300 miles before your next oil change. It might take a few oil intervals, but Sea Foam in the oil will reliquefy deposits and help the rings return to normal performance. If the dieseling is related to this, that will help.

5 months ago

According to the Champion spark plug website, dieseling is caused by too hot of spark plugs. I put cooler plugs in a 1972 427 and it solved the problem.