Guidelines for replacing thermostats in 10 easy steps

Most drivers only become aware of a thermostat problem when the cabin heater isn't working as well as it should. There are few issues with thermostat reliability or the installation of replacements. Thermostat failure is usually mileage and age-related. Gates recommends to service thermostats preventively and to also replace old gaskets and seals with new ones.

Here below you can find general guidelines on how to replace car thermostats. However, remember to always refer to the vehicle manufacturer's recommended procedures for replacement and maintenance of thermostats. 

When car thermostats fail there are two scenarios

If the thermostat becomes stuck in the open position, there is continuous flow of coolant into the radiator causing the engine to run cold. Overcooled engines run inefficiently, which leads to increased fuel consumption and higher emission levels and engine parts enduring more wear. In addition, the car interior will not heat up properly.

If the thermostat becomes stuck in the closed position, the circulation of the coolant is blocked so the coolant cannot get to the radiator to be cooled which causes the engine to overheat.

How to install thermostats in 10 easy steps


Safety first
Always wait until the engine is cool before working on any part of the cooling system.


Remove the hose attached to the thermostat.
Be aware that a considerable amount of coolant can pour out of the hose when you take it off.


Look at how the thermostat is positioned.
Before proceeding, make sure you are familiar with the configuration and remember to put the new thermostat back the same way.


Loosen the bolts and remove the old thermostat.


Remove the old seal/gasket or old sealant remains and make sure the mounting surface is clean.


Before installing the new thermostat, inspect the other cooling system service parts: coolant hoses, water pump and pressure cap(s).


Install the new thermostat so the copper heat-sensing element is toward the coolant flow coming from the engine. If installed upside down, it won’t function.
Old gaskets and seals should be replaced by new ones. Carefully follow installation instructions. Only apply sealant if specifically recommended by the vehicle manufacturer. Put an even bead of sealant along the edge of the part, but don’t use too much sealant. If you do get too much sealant on the part, wipe off the excess before mounting the new thermostat. Too much sealant compromises the correct installation and will break off within the cooling system, contaminating it. Sealants are also made with different drying rates, so respect the sealant's printed instructions.


Tighten the bolts evenly to the manufacturer’s torque specifications.


Re-attach the hose.


Do a final visual inspection to ensure there are no leaks after the cooling system refill.
Keep in mind that some leaks will become obvious when the engine is cold, but others only when it is hot.