I have a 05 black cabrio and decided to paint the cowl vents a gloss black to match the paint instead of the dull plastic look. They looked great for about a week then the paint began to chip off. Yes, I sanded and primed them before adding a high quality black paint, sealing them also with the traditional clear coat. Actually, 5 coats of clear!

I'll let them go for now through winter. Come spring I'll have to face a replacement problem. Bottom line. Painting those things is a bad idea!!!

 

Did you use an adhesion promotor (ad-prom)? That's the norm for painting plastic, as I understand it. Nice idea though. These cars have way too many different colors and finishes fighting with eachother.

 

Just clean them up and spray with clear coat. No paint. They become nice and black and shiny.