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!

[CTScott]

It may actually just be a bad temperature sensor.

[bart27]

Hi, Thanks for your reply.
If it is a bad sensor, would that make it overheat into the overflow bottle? or would a bad sensor just give false readings?

[IllusionX]

The overflow liquid rises when the water heats up. Water expands when hot and will siphon from the overflow when it cools down to prevent air getting in the cooling system.

CTScott probably can confirm this, but AC should turn off automatically when it detects overheating temperatures.

Sent from my A0001 using Tapatalk

[bart27]

Ended up being a head gasket or cracked head. Being that it has 330,000 miles on it I am replacing the whole engine.

Thanks for helping.

[zru344]

How was it determined that the problem was the head gasket or cracked head? Having the same problem. Thanks.

[nortonfb]

You can't really tell until you have the head off. You can check along the head gasket
looking for signs of a leak, white smoke in the exhaust, bubbles in the radiator.
Get a pressure test done. Symptoms would be pretty much the same.
Check your error codes. Look at your oil if it's white and frothy most likely bet is
the head. Either way the head must come off.

[Bluevitz-rs]

A head gasket can leak and push high pressure combustion gasses into the cooling system pushing out coolant into the overflow until there isn't enough coolant to sufficiently cool the motor.

[zru344]

Ok. Thanks for the replies. I think I do have some oil stains along the head gasket area. I'll have it checked.