So I'm going to do amsoil powerfoam this evening. I did it last time during the day and won't be doing that again (everyone in a two mile radius was about to call 911 on me...i figure noone will see all the smoke at night). I only let it soak for 5 minutes the first time and did it on a cold engine so I don't think it was very effective. How long should I let it soak for? Bottle says 10-15 minutes but I've heard of people leaving it in there for a couple hours. I'm going to change the oil the day after. doing in an engine flush too before changing oil.