I spray engine bays a lot...heres my tip...blow out engine bay with air compressor...get wax and grease remover...this is critcal..wipe down all areas so they are so clean youd eat of it...next get 3m red scuff pad and scuff the surface to be painted real good...if your really pic I suppose you could wetsand it with like 500grit but for a engine bay red scuff will work...wax and degrease again..blow down with air compressor..next just spray what ever color base coat your car is in the bay. You can use "basefix" as a clear if you choose or real clear or just leave it in base coat will be fine.
I really wouldnt use any aerosol stuff on a engine bay or really anything