i asked this question the tempture gage shows it is over heating but the engine is cold to touch
A bad water pump or thermostat can cause an engine to overheat. A plugged (clogged) radiator or heater core may also cause an engine to overheat.
The answer will depend on what engine it is and what it is being required to do.
The engine is overheating.
A Caterpillar see seven diesel engine will begin to overheat at a water temperature of 210 degrees. The recommended operating water temperature is 180 degrees.
If your engine thermostat sticks open it will run cooler on your temperature gauge and you won't see the temperature gauge go up to the point where your engine thermostat opens and then the temperature gauge will show a drop in temperature , your check engine light will probably come on , your gas mileage will be less , the heat from your heater probably won't get as hot If the engine thermostat were to stick in the closed position your engine will overheat ( but there are several other causes for an engine to overheat )
Air inside engine
generally if an engine overheats, but then does not overheat when heater is turned on, is a good indication that the engine thermostat is stuck and needs replacing
Turning the heat on would actually lower the engine temperature. It's a well known trick if your car starts to overheat. Having the A/C on causes a power loss to operate the compressor, which would also cause engine temperature to go up due to the hot air from the condensor going through the radiator.
The lack of air intake designed to flow into the motor.
The engine will overheat and the pistons will seize.
Low fluid levels in engine.
The 2006 Toyota coolant temperature sensor is located on the front of the engine. The coolant temperature sensor will be a few inches above the thermostat housing.