okay so I have a 91 NA. It runs great. Driving around toen for less than an hour, no big deal. Never gives me problems. It never loses coolant. Held pressure under a pressure tester. I drive to and from work everday for 2 months never overheats. I was driving across town (2 hours approx), and half way there on the highway the temp gauge went up 2 notches higher than normal, stayed there for about 20 seconds and then shot for H with no hope of bringing it back down. Towed home. Refilled the engine with coolant, bled the air out of the system and success. I'm running again. I have good coolant flow. You can feel the temperature difference from the inlet and outlet of the radiator so I now it is cooling. The fans work fine. They are always running when it has overheated. I replaced the thermostat and radiator cap because they're cheap and easy to replace. All OEM parts. Even after that it's still overheating whenever I run the car for about an hour or more. It will do it faster If I'm racing on the hoghway. Was going 110 side by side with another 2 and it overheated in 15 minutes! Its driving me crazy. Any suggestions? The only thing I can think that I haven't verified or replaced is the head gasket, but I'm not loosing coolant, and its not smoking. Its been suggested by a toyota guy though so I'm looking into it. It's not that I doubt his diagnosis, I just don't want to pull the motor that far apart when I don't understand exactly how the headgasket is causing this problem. HELP!