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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!
 

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Wanna_turbo said:
...Refilled the engine with coolant...


...I'm not loosing coolant...
:confused: It is going somewhere.
It is a terrible idea to be going 110mph in a car that has coolant system issues. :slap: ...are you trying to create more problems with the engine?

If there is no air in the system the coolant is either blocked, or leaking out of its normal pathway.

HG issue, cracked head or block is possible.
Drain the oil and see if there is coolant in there.

Have you done a compression and leakdown test? ...that is the next step.
 
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I refilled with coolant because it all blew out through radiator cap. It doesn't leak out while i'm driving.

If I let it sit until it's cold again then the vacuum valve in the cap works and the system refills. I don't have time for that though so I just put new coolant in it so i can get home without a tow truck. I wasn't worried about driving at 110 because i thought the thermostat/cap had fixed the problem. It's been real intermittent. I know i still have some checks to do for the head gasket, I want to know if anybody knows why the head gasket would do this assuming that i'm not overheating because of low coolant (leaking into the combustion chamber).
 

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BHG, the coolant is leaking into the combusion chamber. Check if ur tail pipe is emittin white smoke when the car is warmed up.
 

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2damaxmr2 said:
BHG, the coolant is leaking into the combusion chamber. Check if ur tail pipe is emittin white smoke when the car is warmed up.
Im with him ^^^ I doubt that it could be anything else. I suggest you go ahead and change you head gasket now before you end up with bigger problems.
 

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Do a compression test with the car warmed up. If that looks good then try a leak-down. If all of that passes, it might be time to think about your water pump.
 
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