The temperature gage started fluctuating between midway up to the red zone yesterday while driving in traffic. At highway speeds it was still wavering, but not up to the red zone.

Today I replaced the thermostat, but the temp is still unsteady. I noticed a little steam around the radiator cap while at idle with the AC on. Both fans were operating constantly.

So what makes the temp waver like that if not the thermostat? Could a leaking radiator cap cause that?

See if the link below helps:

https://www.askmehelpdesk.com/cars-t...tml#post235973

This is important when filling coolant in your Camry. You may assume the coolant level is full when it reaches the top filler neck.
But the block has not been filled. Now you have a HUGE air pocket in there, hence the steam at the cap.
To do correctly, fill to the top, now lightly press on the top radiator hose to make it as straight as possible. Pour coolant mix slooowly!
You see, the coolant can't make it over that hump in the middle. You will now be able to put 3/4 more gallon in there and the entire cooling system will be full.
It will need to be constantly burped until the cooling fans come on.

Attachment 10928

The temp gauge is going all the way up to the red, car is running hot, then the temp gauge drops back down. Drove to work which is 25 miles one way car got hot, coming back home the same, I let the car cool and added more water, because it was coming out of the overflow, then drove to auto parts store about 2 1/2 miles and back home and the gauge stay where it was suppose to, it didn't run hot. Waited awhile had to go off and got on interstate and the temp started rising again. In 2010 I had put on a new water pump, timing belt, hoses and thermostat. Any help you can give will be greatly appreciated.

Bob

Hopefully, the head gasket has not blown. Coolant being forced out of the overflow is often a sign of a blown head gasket. If that's not the case, replacing the radiator and refilling with a 50/50 mixture of antifreeze and distilled water should solve the problem. Phosphate scale is likely blocking many of the internal passages. Be sure to properly purge all air from the system--read you Owner's Manual on how to do it.