Someone suggested timing and that would be where I would look. I had that problem once and it drove me nuts. My timing was right according to the light. What I forgot to take in account is the timing has to be set at the correct RPM. I couldn't cool the car down no matter what I tried. I put a tach on the car and found my idle set too high. I adjusted the idle down a few times and reset the timing while doing it. Car ran cool and fine after that. You've tried everything else, check your timing. My .02c worth.