Years ago, I ran a vapor degreaser. It's a tank with steam coils at the bottom that are covered with trichlorethylene, which vaporizes from the heat. There's a cold water jacket around the top that condenses the vapors and keeps them in the tank. You lower greasy oily parts into the tank and the vapors condense on the metal and run off, taking the grease and oil with them. There's also a spray wand to help it along.
I'd lower an engine block into it and get it as clean and hot as I could, then lower it into a vat of dip cleaner and watch it bubble and boil for a half hour. Then it went into another vat, this time mineral spirits, and finally back in the vapor tank for awhile. After that, it was sparkling clean.
Before modern motor oils existed, there was a lot of trouble with sticky hydraulic lifters. My cure was to dump a couple of quarts of carbon tet in the crankcase and let the car run outside for an hour or so, then bring it in and change the oil and filter. Worked great.