Yeah, I forgot to mention: I ran a 160* thermostat with an 1/8" hole dilled in the flat part (not the moving part). I also retained the stock "non-pressure" cap, so I guess I had a "zero" pressure system. So what? it worked, even in California heat. The engine never got above 190*.
OCK is right, GMC's are famous for trapping air and cracking the head, so be careful.........
