Paint didnt Adhere Correctly? Why?

[Subzero]

Lately I've been painting the frame/ engine bay while the engine is out for a full rebuild. I got all the thick layers of grease off everything first. The frame is going well but the fenders are not. I sanded down the existing paint very far and in some places to bare metal to remove what rust was there. After wiping with mineral spirits, I then sprayed Eastwood Rust encapsulater. After a few coats it looked great. I waited 3 hours and sprayed VHT engine enamel gloss black. Some spots looked good while others were ashy looking and rough, like the paint didn't bond right. The problem areas were directly exposed to sun all day and got fairly hot, could the metal have gotten too hot and the paint didn't adhere correctly? Other areas that weren't directly hit by the sun look great. I had to sand everything again so it's smooth once more. The truck is parked in a back lot behind the shop that removed the engine with the hood off and a tarp over it when I'm not working.

[chad67]

Paint is very sensitive to temperature, that's why they sell reducer for different temperature ranges. To get paint to lay right in direct sun, you almost have to pour it on.

[HIO Silver]

Rust encapsulator is not UV stable. It requires a top coat or needs to get covered by carpet and stuff.

[Subzero]

Yes I'm putting the top coat of gloss black over it for the fenders and for the frame I'm using Extreme Chassis Coat high gloss. The frame is looking awesome but these fenders are a pain . In my experience high heat engine paint is harder to use than normal auto paints. Could I use normal auto paint on the inside fenders or would the hot coolant hoses and exhaust heat burn it up? I'm using headers if that makes a difference. Tomorrow I'm going to try and paint early before the hot sun gets out but I can't paint till the shop opens at 8 am. I was tempted to pay someone to paint this at first but now I'm glad I'm doing this because it really gives a sense of pride even if it doesn't look as good . I can't wait till it's back on the road

[Subzero]

I sanded all the engine enamel paint off that didn't bond right and tried something else- using the chassis coat gloss paint on the fenders. It looks great, and I'm very pleased with how the trial fender turned out. It's very tough paint and should hold up well, much better than engine enamel. Only problem is that is $19.99 a can . So all is well now and I should be finished painting by the end of next week.

[Ranchero50]

I don't think I would have used a gloss on that application and it doesn't have the correct sheen. Ford used left over paint for many black parts. My '68 Fairlane has metallic black on the shock towers. I did my truck's in a satin black and it looks period correct. I know looks are purely subjective so build it as you want to.

[tac]

There is a thousand reasons paint doesn't stick. To dry, not dry enough, temperature, humidity, contamination, paint incompatibility, but my the red flag to me would be using mineral spirits. I wouldn't chance using anything that leaves a residue behind before putting paint down. This is probably ok if you are using an Oil based paint but not anything else. Stuff like this can screw with undercoats or float up thru them and make a top coat peel off.

[guhfluh]

I like a high gloss black on under hood and chassis parts because it cleans MUCH easier, doesn't stain, etc. The originality of the color doesn't bother me that much. I even really want to do the firewall as well for the same reason, even though it's originally painted.