I added it to the oil in my 170K mile Dodge Dakota, it it not only knocked loose a TON of sludge, but when I pulled the oil pan to clean out the sludge, the paint on the INside of the oil pan can off while I was wiping the pan clean! Not sure I want to leave it for a long time in oil again, but I do use it in the gas, and pour down the carb. I found it for using on my 30 yr old 2 stroke boat engine. It creates a smoke show like hell has come down to earth in the boat motor, and has liquid carbon running out of the exhaust for days after using it, so I know it works. I also know it works because I used a small amount in a bowl with a toothbrush to clean carbon off of spark plugs, and gasoline/carb cleaner/ kerosine/ anything else has not worked as completely or effortlessly as Seafoam to do this. I can only find the stuff at NAPA .