Have my engine out so figured it's a good time to paint the bay as well. I plan to clean and degrease and then am unsure if primer is necessary seeing as it's not going to be down to bare metal. Can it just be roughed up with some sand paper after cleaning and then painted? It will be going from factory dark red to black so coverage shouldn't be an issue, I'm just unsure regarding the need for primer or not. Thanks!

 

I would sand then hit it with primer.

 

I would prime it. I've never had terribly good luck with just paint over paint.

 

Degrease it several times. Scuff it at least and then spray Epoxy primer.

 

Thanks guys, sounds like primer is the way to go.

 

I agree with Tibo.

A good epoxy primer for a good price is Omni MP170. You can mix it 2:1:1 (2 parts epoxy primer : 1 parts MP175 catalyst : 1 part Omni MR186 Reducer) and it will spray out like a sealer, and flash off fast. You can paint right over the top of it within 24 hours without having to scuff it. Omni is PPG's lower end line, but that epoxy primer is actually great stuff to work with. It calls for a 2:1 mix without reducer, but sprays heavier, and takes longer to dry. Mix it my way and you'll love the stuff. 1 coverage coat is all you need.

BTW I am a certified PPG painter at a body shop....been doing this a long time. If you have any questions, dont be afraid to ask

 

I agree with this. Reduce the Epoxy primer to use as a sealer and paint over the next day with top coat and no need to sand in between. If you are going with straight black, single stage urethane would work well. Lower end lines like PPG Omni or BASF Limco are fine for undersides/engine bays. No need to go with the expensive stuff. Save that for the outside.

 

This