[eschaider]

Joel,

Your underhood air temps are probably higher than you suspect. Use one of those cheap Harbor Freight laser thermometers to measure the heat of the fuel pressure regulator (FPR) after you have been driving for a while in that 95˚ heat. I think you might be surprised.

What Morris has said about the tank venting is true. It probably occurs through the charcoal canister. Make sure you venting valves and canister are working. Even when they are you will still build some pressure in the tank but it should not force fuel out the filler cap.

A couple of thoughts on charcoal canisters. A charcoal canister is a part of your car’s evaporation control system. It is designed to prevent the release of volatile organic compounds that escape from your fuel system and engine. Charcoal pellets in the canister absorb the harmful fumes from the car’s fuel system and store them. Later these fumes are burned by the engine while it is running.

A blocked or inoperative canister system will not vent the vapors to the engine for burning. The lack of venting will increase pressure in the fuel tank. While not a sure bet, the blockage can raise fuel tank pressure. Is it enough to force fuel out the filler cap — I'm not sure, but a check of the system could either eliminate or identify it as one of the problems.

I know it sounds silly but do the laser temp test on your FPR after driving around in the AZ heat. You might just be surprised. While you are at it get on your back and also check the fuel tank. The fuel tank check will either eliminate it as a potential problem source or identify it as a potential problem source — either way good to know information.