2008 Yaris Overheating

[bart27]

Hi, my 2008 Yaris keeps overheating, I’ve changed the water pump, thermostat, radiator and even the radiator/filler cap and used Toyota coolant.

I drive a long way back and forth to work (100 miles each way) and sit in LA traffic.

After about 80 miles the thermostat light will come on with or without the AC running and it happens both in the early morning (5:30am) when it is cool outside and in the afternoon when it is hot outside. I can tell when the light is about to come on when I have the AC running because it stops putting out cold air. I would turn off the AC and the light would disappear but when I get to a stop light it would come back on. I have tested it driving home with and without running the AC and the light still comes on. The fan is working and comes on when it starts getting hot and/or when I turn on the AC.

I have checked the engine compartment for any sign of leaks and found nothing. If I empty my overflow bottle, then drive to work it will be full. I drained the overflow bottle and filled up the radiator with the same amount of fluid that is in the overflow bottle and it tops off.

I am at a loss as to what it can be. Is it the fan? The AC condenser? The AC compressor? I don't know. How to I test these options?

Thanks for all your help!