I would like to paint he inside (for oil drain back)and the outside of my block (car color paint) . What do you use for primer ? Is inside different from outside ..... thanks for your time .... DTM
I've painted the inside of engine blocks with Rustoleum red oxide primer too. Not sure how much it helps with drain back, but it seals the casting and might make it harder for sludge to form.
More of a detail item that's nice to do, rather than something that you need to do.