Overheating at low speeds

I have a 3 speed auto '89 Corolla hatch and am having the opposite problem than most with my temp gauge. When I'm idling or driving at low slow speeds the temp gauge maxes out to a centremetre past H, but there's no effect on the car at all, and when I cruise, even at hgh speeds, the temp goes down to very normal. While I'm quite certain that the car is in no way overheating, it is still disconcerting to look at the gauge that high. Does anyone know anything about this problem? Is it common? Does it matter?

Thanks for any help

Neale

WAG: thermostat about to collapse? (Ie, coolant is still flowing through the radiator but the thermostat is not opening or closing very well. Extra speed == extra cooling, despite low flow rate.)

Hi Neale:

You may have a clutch fan that is inoperative, loose fan belt (sometimes they don't squeal when slipping), bad water pump, plugged or restricted radiator tubes, or a bad cap. It does certainly matter Neale, a warped cylinder head or worse may occur. If you overheat your vehicle it usually ruins the wax pellet in the thermostat and you must replace it. There are a few made now that when overheated they remain open instead of closed. Make certain that you install any new thermostat correctly. There is a right side up and down in the housing and in some applications an orientation for flow. Best of luck.

Bigfoot wrote:

I would be very careful here. Just go ahead and replace the thermostat. It's a cheap part but very important. How well has the car been maintained ? Cooling system been flushed on a regular basis ? Your radiator could be clogged, waterpump going out.

This sometimes happens when the coolant level is low. Have you checked that part of it?

Hey Neale

My dad has a 90 Corolla 3 spd auto and he had the same problem While sitting idling, the temperature gague would go up, not as high as yours but it would go up and you would all kinds of heat, and it was nice. BUt when you were driving, it would go down to the point where there was basically no heat! So dad tore it apart and found out that it was indeed the thermostat! Once he changed it, the Gauge now rests at half way up idling and driving!!

I'd try that first. Chris from Canada