I've been trying to paint my engine cover for DAYS and I'm seriously getting pissed off. The problem is the paint won't stick to it. I've used high temp primer and I've used adhesion promoter, I've sanded the surface, I've pressure washed it etc. However, every time I go to put masking tape on the parts I've already painted the tape just peals the paint right off. This is so incredibly frustrating, I'm about to just throw the whole damned thing away. What the hell am I doing wrong?

 

Paint choice!

 

^ yup

 

Are you painting it in a high humidity environment?

 

I'm using a high temp paint from duplicolor suggested in this thread:
https://www.rx8club.com/series-i-tech-garage-22/diy-engine-cover-painting-128089/
Should I use paint specifically made for plastic instead? Will it blend? um.. I mean will it bubble/crack/peal in the engine's heat?

Nope, Arizona -_-

 

You might try Rustoleum. It's formulated very differently than other spray paints. The cheapo aluminized plastic "chrome" was flaking of my Solara grill ~ 5 years ago. I tried at first to get the aluminized junk off with no success, then just painted it with black Rustoleum and let it bake in the sun for a day. Not one chip in spite of 5 winters of road salt sandblasting.

 

The problem sounds like its most likely the undercoat. While the manufacturer may claim it sticks to plastic simply because it doesn't slide off, that doesn't mean it will last for any period of time. You either got a low grade undercoat, contamination, like plastic dust from not being washed after sanding, dirt or moisture (which sounds unlikely since you seem to be taking some care in what you are doing,) or an adhesion promoter chemically intended to be for metal, but the manufacturer claims otherwise. Go to www.thecoatingstore.com/Types_of_car_paint.html to learn more about high temp paints and more about undercoats and adhesion promoters. And definitely do some research on the adhesion promoter you are using to ensure its chemical make-up is intended to be used on plastic.