A thermostat controls flow of coolant in a vehicle’s cooling system. It opens or closes according to the temperature of coolant when a vehicle’s engine is running. If it stops working it can be stuck open or stuck closed. It will result in high temperature of the engine, damage to the radiator or crack in the hose.
You can test a thermostat with simply boiling water. It is simple and easy.
1- Boil water in a metal pan and dip thermostat in it.
2- If a thermostat is working then it should move to open in boiling water. If it does not open it is ‘stuck closed’ and if it stays open but does not close when taken out of hot water it is ‘stuck open’.
3- If thermostat doesn’t work properly it needs to be replaced with a good one. You can search internet to search the right part number for your vehicle. You will also need a gasket to prevent leakage.
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5- When engine warms up thermostat opens to let the coolant flow.
6- When thermostat is taken out of hot water it again start closing.
I hope this article be helpful.