I know I can use carb cleaner, but was intrigued by a suggestion online to use automatic transmission fluid (ATF), especially since I have a leftover bottle of the stuff.
I fully intend to try it out and update this with an answer, but meanwhile would be interested to know if anyone else has ever tried this option.
Yes, ATF is highly effective at cleaning carbon, but Marvel Mystery Oil is even better (it's ATF mixed with dry cleaning fluid). If cold, allow the fluid to sit for at least two days, then spray with carb cleaner. The longer, the better -- many guys have freed frozen piston rings without disassembly by letting the fluid sit for weeks.
The warmer you make the parts, the faster it cleans. I've personally cleaned heavy deposits from piston crowns on a warm engine in a mere 10 minutes. Old, salty marine mechanics will warm an engine that is not running with heater coils or by pumping hot water through the block.
Used it a lot back in the early 70's, seemed to be common knowledge in all the Dealerships and was Very effective at removing carbon deposits on the pistons and cyl. Head areas.
Much more efficient and effective (and you are sure the waste is disposed of) to take it to a machine shop with a high temperature chemical cleaning machine.
