Car Thermostat – Cause of Over Heating?

I have a question for you Mr. Mechanic.  My Toyota Camry, seems to want to over heat when I sit in traffic for long periods of time or when idling with the A/C on high. My mechanic says I should replace my thermostat to solve this issue but I am questioning his ability to properly diagnose the problem as he says “it’s no guarantee”. What say you?

Mrs. Lilly

Hello there Mrs. Lilly,

Have you watched my overheating video yet?  I will place it below my reply below, please watch it. I would agree with you with your hesitance in replacing the thermostat to resolve this type of overheating complaint.

Usually, usually the thermostat is not a big concern in overheating issues as it is pretty rare that the thermostat goes bad on its own.  Usually, usually overheating issues when sitting still in traffic or at idle is due to a bad electric cooling fan issue either a bad motor or a bad relay or temperature sensor  controlling the motor.

And, usually we do not replace the thermostat as regular maintenance until we see a reason to do so or we are doing another cooling system repair (replacing the radiator for example) and it would be wise to replace the thermostat during that other repair.

What is sounds like in your case, there is an electric radiator cooling fan under the hood up near or on the radiator itself that is needed to pull air across the radiator when the vehicle is not moving or not moving fast enough to circulate air naturally across the radiator.

This electric fan should cycle on and off as the engine heats up, but is rarely used when driving at freeway speeds as there is plenty of air flow naturally occurring.   Using the A/C just adds more of a “load” to the engine and produces more heat so that cooling fan has to be on. Check it yourself, open the hood and turn on the A/C and watch the temperature gauge and fan motor operation.

You might have 2 fans, one is for the A/C compressor and helps pull air across the A/C condenser (looks like a small radiator in front of the actual radiator) and one for the radiator itself.  You will probably have both fans running if equipped with two during this test.

Also, I should note if the coolant is low inside the radiator it will not signal the cooling fan sensor of the coolant temperature so check the coolant level first.  If the coolant level was pretty low, you might have  a coolant leak somewhere that should be repaired first.

Here is the engine overheating video, take a watch.

To recap

1. Check the coolant level inside the radiator and top off

2. Check the electric cooling fan motor – should be coming on and off as engine warms up

3. Check for a cooling system restriction in the radiator reducing the circulation of coolant