I have a 1995 Camry, had a corroded freeze plug fail. Replaced freeze plug, and coolant. My problem is, I will drive down the road, all is good, the temp is mid range and the heater works like a champ. A mile or two into the drive, the heater starts discharging cold air, then the temp starts rising. In about 30 seconds the car is overheated. I will then pull over and run the engine up to 2000 rpm the temp comes down and once again the heater works. I can repeat this problem easily.
My guess was the cooling system has an air bubble.
WHAT I HAVE DONE SO FAR
I tested the thermostat (on the stove with a very accurate thermometer),refilled radiator leaving the cap off and adding more distilled water and antifreeze after each time the radiator pukes some out as the engine idles. This took about 40 minutes but finally the puking stopped and I have fairly hot water flowing accross the radiator (finger test). Put the cap back on, test drive, same problem. I have no leaks, or fluid loss, and no water in the oil. The fans work when I put on the air conditioning, but I’m not sure if they work without air conditioning; however I would think that would have nothing to do with loosing heat in the car. Any suggestions, I am loosing patients and I can’t afford to loose any more hair.
You might not be getting all the air out of the cooling system.
Try this, get the engine up to operating temperature, and with the engine idling, loosen the upper radiator hose clamp at the radiator just slightly. Slip a flat blade screwdriver between the hose and raditor neck. let any air in the cooling system purge out.
Tester
Could the thermostat be in backwards? Some have a small hole so that coolant flow doesn’t completely stop when the thermostat is closed. The small hole would allow a little coolant flow even if the thermostat were backwards.