Overheats then cools?

[hcorea]

I have an na 91 supra and I had to drive on the freeway extensively today and I noticed that it would seem to overheat then suddenly drop to normal temperature. It would also overheat on idle and then begin to drop back to normal temperatures once I started to rev it higher on the road. My friends said its a fan kicking it but I don't really know anything about cars. Also I just turned up the ac to high and the temperature never climbed again. Whats going on?

 

[charman02]

I have an na 91 supra and I had to drive on the freeway extensively today and I noticed that it would seem to overheat then suddenly drop to normal temperature. It would also overheat on idle and then begin to drop back to normal temperatures once I started to rev it higher on the road. My friends said its a fan kicking it but I don't really know anything about cars. Also I just turned up the ac to high and the temperature never climbed again. Whats going on?

I've had situations like that before, and it's always been that there's an air pocket in your cooling system. I'd probably try to bleed your cooling system for any possible air pockets.

 

[ms07s]

Air in the system is most likely the case. It could also be a bad t-stat or fan clutch.

 

[GrimJack]

You need to check all the usual cooling system issues.

Radiator cap and thermostat should be replaced, this is cheap and easy to do. Pull off the two top radiator mounts and pull the radiator away from the frame, check that there isn't a bunch of junk trapped in front of it blocking the airflow.

Make sure that you're not running too much antifreeze in the mix. Check that the fan clutch still works.

If all this checks out and the problem persists, get a block check done to look for a blown head gasket.

 

[Cycoclown]

i run in the summer 70% water and 30 antifreeze. before the summer started. i replaced alot of old squishy coolant lines.. what i would do is buy a new thermastat and cap. and burp ur system... its so easy.... a cave man could do it..

 

[dopeassjackson]

i have found that with other toyota engines is your not useing a genuine toyota T stat the gauge will go in the red then come down and fluctuate alot up and down. i then installed a toyota T stat and it would go up to temp quicker and never get higher.

 

[88_7mge]

my 88 NA used to do that driving it hard. Once i got out of it and drove normal the temp gauge would climb to over 3/4 then drop back down. Start by replacing your thermostat (extremely cheap, and never a bad idea IMHO) then jack the front of the car up to make sure that your radiator cap is up higher than the heater core *stupid toyota design on most of their vehicles. Then run your engine until it gets up to normal temperature to get all the air out of the cooling system,*heater should be turned all the way up and vents blowing.
The reason you need to jack the car up is because toyotas design on the cooling system has the heater core as the highest point in the system, why sometimes if there is air in the system it sounds like a river behind the dashboard.

 

[jdub]

i run in the summer 70% water and 30 antifreeze.

Mind explaining the reasoning behind this?