Hi. I have a 4 cyl 2003 Toyota Camry and I just replaced the thermostat and o ring.
While driving it late yesterday evening it began to overheat. We had been driving for about 3 hours with no problems. The temp gage stayed stable right in the middle..then would quickly go up toward overheating and quickly come back to the middle of gage...
When I stopped the car, water could be heard gurgling but I didn't remove the radiator cap because of fear of being burned. That cap has a LOT of pressure behind it, even after sitting..unrunning..for hours!

What could the problem be?

 

Did the engine overheat before the repairs?

Did you purge the coolant system of air after adding coolant?

Let the car sit overnight to cool off. Check coolant level in the overflow tank. If no coolant in tank, remove radiator cap and check coolant level. Top off both radiator and tank.