Ok it seems since I've installed my Fluidyne radiator, I've been having constant overheating problems. I'm running a 1/2 size fludiyne radiator with a 12" pro form slim fan. I also installed a new oem thermostat. My cars been overheating whenever I go on the highway. Temps rise to the midpoint and continue to rise unless I turn on the heater, which drops the temps almost instantaneously. This doesn't happen when driving at low speeds. What's the problem?