The only time that you should run a car without a thermostat
IS IT OKAY TO REMOVE A CAR'S THERMOSTAT?
Many people have asked whether it is good to remove the thermostat in their cars, especially those in hot climate regions. The answer is simply NO! It is not good. But there can be cases of emergency when the thermostat is stuck closed and the car needs to be driven to a workshop or home. In this kind of circumstance, the thermostat can be temporarily removed if it is easily accessible.
For fuel economy and engine longevity concerns, the best thing to do is to have the engine's thermostat fixed in place in the engine. This can make the rings to last long and make the engine to deliver better fuel efficiency as the engine will operate at its optimal temperature.
Where proper preventive maintenance of using coolant solution, replacing the coolant and replacing the thermostat periodically is not done, it can resort to a stuck closed thermostat which eventually will cause overheating.
Thermostat removal should normally be a very temporary measure until you can get the cooling system fault diagnosed and fixed.
In the case where troubleshooting is being carried out on the cooling system, thermostat removal can be done temporarily for the purpose of identifying the fault culprit and then returned back to the engine when troubleshooting has been completed.
THE NEGATIVE EFFECT OF REMOVING THERMOSTAT PERMANENTLY:
It will take more time for the engine to attain operating temperature from cold start. The engine will also be over-cooled during highway driving in a cold weather. The natural cold air passing through the radiator will be sufficient for the cooling and might even over cool the engine. The practice of permanent thermostat removal also reduces engine longevity due to increased wear as a result of the engine not reaching optimal temperature in time or never reaching optimal operating temperature at all.
Removal of thermostat is not a standard or recommended practice. It should be done only during emergency when overheating situation has left one stranded on the road or during troubleshooting.