i got a tough one for you. i have an 89 gl that has an intermittant overheating problem.when i it start it up ,and sometimes when i accelerate i can hear water wooshing thru the heater core.it dosnt overheat all the time.today i drove it 5 miles it overheated. i let it sit then drove it 40(freeway) miles and it was fine.after sitting i drove it around 20(freeway) miles and it started overheating again i pulled over let it sit drove off and it overheated again.i let it sit then drove off it ran fine the rest of the way home(in traffic). there dos`nt seem to be any rime or reason to this.ive already replaced the thermostadt. any ideas? thanks rob

Could be air in the system. Does the heat go cold?

 

Look for bubbles rising in the radiator with the cap off and running. Mild overheats are ok, but after the 34d or 4th time, you could have compromised the head gaskets. Bubbles would be indicative of a hg, if not too bad can be held off by a liquid glass (sodium silicate) type block sealer until you plan for HG job.

 

But first, there could be air in the system from replacing the thermostat. It's a good idea to fill the block by the upper hose or into the thermostat housing before installing it.

 

Did you have overheating or warm operation before doing the thermostat?

 

Is the thermostat the proper size, or a cheaply stamped aftermarket that does not flow as well as an OEM?

 

Check for green corrosion and loose fins on the radiator.

 

Check that the cooling fan is operating at temp or whrn warm. You can test it by jumping the terminals at the thermoswitch on the radiator.

 

The heat should be on, and hold the idle up while adding coolant, and make sure that the thermostat is open(warm upper hose and radiator) before calling it done and installing the cap.

it was doing the same thing before i put the thermostadt on. i had been watching the temp gauge so i pulled over well before the red zone.no leaks the heater blows hot.i had never heard of bleeding the cooling system so im going to give it a try.