How to Replace a Car Thermostat

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The thermostat is critical to your engine’s health. Although this device is small in size, it plays a huge role in the cooling of your engine. The thermostat works as a gate between the radiator and the engine. When you start the engine, the thermostat stays closed, blocking the coolant that’s trying to flow to the engine, which allows the engine to warm up quickly so it can perform effectively. Once the engine reaches an optimal temperature, which is an average of 200 degrees Fahrenheit, the thermostat opens to let the coolant through, keeping the engine running cool and preventing it from overheating.

When a thermostat goes bad, it can get stuck closed or open. When it gets stuck closed, the engine can overheat and sustain damage. All cars have thermostats; however, the location can vary slightly. Your thermostat may be located on the top or bottom of your engine. If on the top, then the top radiator hose will be connected to it. If your thermostat is in the lower part of your engine, you can find it by following your lower radiator hose. To test your thermostat, start your engine and grab the hose connected to your thermostat. If the hose stays cool for approximately two minutes, then quickly gets warm, your thermostat is doing its job effectively. If your hose immediately starts gradually getting warm, without staying cool for a few minutes, then it is stuck open. Finally, if the radiator hose stays cool the whole time and doesn’t warm up, then the thermostat is stuck closed, which also means your engine is about to get too hot. The process is the same for most cars; the only thing that can vary is what you will have to remove to reach the thermostat. If your thermostat is indeed faulty, then read on to learn how you can replace it yourself.

Tools Required:

Flathead screwdriver
Pliers
Drain pan
Socket set
Wrench
New thermostat

Generally, if your thermostat is located on the topside of your engine, you don’t need to drain all the coolant in the radiator, just a little bit. However, there is no harm in draining it all, then filling it back up.

Locate the drain valve on the bottom of the radiator. Some cars may have a splash shield on the bottom, so remove that first. If you can’t find the drain valve, you can remove the lower radiator hose and drain from there. Place the drain pan under the hose or the valve, then loosen the valve and let the radiator drain.

After researching the location of the thermostat in your specific car, remove the hose connected to it. If it’s the upper hose like most cars, you won’t need to remove too many components that are in the way; however, if it is behind the lower hose, you may need to remove some obstacles.

The hose is usually secured in place by a clamp. If it’s a worm clamp, use your flathead screwdriver to loosen the screw, and then slide the clamp backwards away from the engine. If it doesn’t have a screw, you will need to use your pliers to remove it. Squeeze the clamp with your pliers and slide it away from the engine.

Finally, pull the hose away from the engine while wiggling it to disconnect it from the thermostat assembly.

Use your socket to remove the thermostat assembly. It is usually held in place by two bolts or more and it looks like a metal elbow. Wiggle it as you pull it off; it will probably be stuck in place. Once you remove the assembly, the thermostat will be sitting right there; just remove it and install the new one in its place. Scrape the old gasket off of the housing.

Install a new gasket, which always comes with the new thermostat, and then tighten the two or three bolts holding the assembly in place.

Connect the radiator hose to the thermostat assembly, then slide the clamp forward towards the engine to secure the hose in place.

It’s always recommended you take the opportunity to put new coolant in the radiator. Fill it up to the top, start the engine and let it run for five minutes, and then refill the radiator to the top.