I had problems last summer with the gasoline expanding in my fuel tank and overflowing the filler neck when the car was sitting in the sun. The tank was not even full.
I have never had this problem before in the 26 years since I have owned the car.
Funky gas? I've always gotten my fuel from Chevron, always Premium.

If you want to reduce underhood heat, an expensive but effective way of doing it would be to have your exhaust manifold ceramic coated. I had mine done by Jet Hot, and I'm very pleased with the result; it noticeably reduced underhood heat, and it looks beautiful to boot. I also had the heat shield coated too.

When I get the Simons sport exhaust for the car, I'm going to have the downpipe section ceramic coated to finish the job.

Bill