Overheating !!!!!


New Member
Jul 1, 2004
Ok I have gone through a big chunk on the forums and found some very useful info, but I still am a bit puzzled.

I have a 90 GT w/ 130K miles.

So far I have replace the T-Stat (180),
Flushed the Radiator,
and Installed an electric fan ( kit from year one 2200 CFM ).

I know for a fact that the old fan clutch was bad, and had hoped that the electric fan would solve the problem. So far no.

The problem is when I am driving. At idle it cools down and runs fine, however when I start driving, ( especially if I let the RPM's get above 2500 ) it starts to heat up. Actually it gets really hot. On more than one occasion the fluid in the overflow bottle has been boiling.

My next part looks like it is going to be a water pump but I am not convinced that is the problem. It seems like I may be loosing coolant but have found no leaks, and sometimes the radiator is full while other times it can be quite empty. My fear is a blown head gasket, but it is also possible that the radiator is bad as it is old.


Thanks in advance,

Casey Vanderville
-- 90 GT in the middle of California.
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i know what you mean man. my old 84 stang would just over heat alot. i replaced the cap, all new hoses, 160 thermo stat, flushed the coolant system, and that still didnt work. i thought the same that the head gasket might be messed up well when i replaced the engine with an 89 it did the same thing. so i swapped the radiator and worked perfectly tell i sold it.
what temps are you running exactly? from the stock gauge or aftermarket gauge?
condition of the radiator?
if you are boiling the mixture, that could be the source of your loss.

ive heard of the shaft on the water pump freewheelin on the impeller - it comes loose.
do a new cap no matter what.

just some ramblings. good luck.
There is a small air dam/spoiler that's supposed to be in place behind the bumper down now under the front of the car. Has anyone removed that? It blocks air and creates a low pressure area behind the radiator under the engine. This low pressure allows air to pass through the radiator and exit the engine compartment under the car. If that has been removed, it often inhibits the flow of air across the radiator because it can't exit the compartment. And the problem gets worse as speed increases.

Given what you've already done, if it's not that, it's likely your radiator. If it's original, it likely has quite a bit of scale/deposits inside that negatively impact heat transfer and that the usual flushes will not remove. Water pumps almost always fail simply by losing the shaft seal which results in leaking from the weep hole. If it's not leaking I doubt replacing it will solve the problem. However, with the radiator out, it's awfully easy to change - and they're not that expensive. So if you pull the rad, I'd replace pump and hoses while you're in there. Good luck with it.
Hey thanks guys for the help.

I will definatley being getting a new cap today.

I don't know about the air dam thing under the bumper. I haven't removed anything, but I haven't had this car that long and the front bumper is damaged a bit from an impact. Nothing seems to be missing underneeth, but I may not know what to look for.

Is there any other way of knowing if my head gasket is blown. It has overheated so many times now that I don't trust it. But I don't really have time right now to do a replacement. I will do a compression test today, and perhaps that will shed some light. Otherwise there is no water in the oil so that is a good sign at least.

As for temp I am only seeing the stock gauge which I know isn't very accurate but I figure that when it shoots up that high it can't be good, even if it is off a bit.

Any other info on how to know if a water pump or radiator is bad would be great too.

Thanks again.

highway speeds = radiator
around town = fan

under high rpm's hoses tend to collapse. and good point about the cap. if it's old it wont hold the pressure like it's supposed to causing the temp to rise. invest in some aftermarket gauges too. at least 1/2 of the stock gauges belong in the dumpster.
something like this happened to my moms old taurus and the problem was the catalytic converters were clogged. sounds pretty weird but we replaced the radiator, thermostat, pump and all that good stuff and nothing worked until we replaced the cats. if all else fails you might want to look into that.
Check the net for a picture of the air dam that should be under the radiator. Did you take the radiator to a shop to get it flushed or you brought some over the counter stuff? Might be best to get a new one all together. I would replace the water hoses just because. Seeing that a water pump is only about 30 bucks and easy to install, that would be on my list and it wouldn't hurt.
about the only way to check the water pump shaft for having come loose is to take it out and check it by hand. at that point, i would be putting a new one in (i mentioned it in case you do everything else and it still is acting up).

rad shop can flow test the rad for ya.

as Michael mentioned, the chin spoiler is important - esp since we dont have a grill. ditto for 4th gen camaros (remember when cars had the aerodynamics of a brick, but had grills to cool that radiator thing). :)

and dont discount the small stuff when you put it back together/renew stuff. proper mixture of water (water transfers heat about 2.5 times better than coolant/antifreeze). if someone put a rich mixture of antifreeze (common misconception that more coolant will cool the car better), that will knock the efficiency down. im not saying any of this is your problem, but when Michael helped me get my cooling system up to snuff last year, it turned out that a lot of little things all mattered.

good luck.