seafoam is like amsoil crankcase cleaner. when i put it in oil, i drive the car to get it hot pull it onto the ramps or where i will change my oil. put the seafoam in it let it idle i repeat idle, for abuot 10 to 15 mins, let it sit for a few, then drain oil till not even drops come out of the pan. amsoil recommends with their cleaner that if you have some miles like 3k on an oil change to change filter first, so that it doesnt knock dirt out of filter into oil, then change it all.
to know if you even have to do that, is to change oil first, put the can in, let it idle for a few, then check it. if its dark there is crap that needs cleaning, if its not, let it drain real good. and marvel mystery is a good safer alternative to seafoam.