Car Thermostat Gone Bad? Here’s How to Replace It

• How do I know if my car needs a thermostat?
• How much does it cost to replace a thermostat?
• Can I replace a car thermostat myself?
• How do I replace my thermostat?

Much like a thermostat controls the temperature of your house, a car’s thermostat helps control your vehicle’s engine temperature. Without it, your vehicle may not warm up properly or will overheat. It’s an inexpensive part, but if it goes bad, it can create expensive problems for your car.

A car’s thermostat is a spring-loaded valve that sits between the engine and the radiator. It’s closed when the engine is cold, allowing the car to warm up faster. Once the car reaches operating temperature, the thermostat opens and lets the coolant circulate through the radiator to cool down.

When a thermostat goes bad, it will either stay open or closed. If it stays open, your car’s engine may not reach a normal operating temperature which will keep it from running efficiently. If the thermostat stays closed, the engine will overheat.

How do I know if my car needs a thermostat?

Engine coolant being poured into a yellow funnel | HUM Images/Universal Images Group, Getty

Once a thermostat goes bad, there are some obvious signs it needs to be replaced:

• The engine overheats, or the temperature gauge shows a high reading.
• The car never warms up, or the temperature gauge changes erratically.
• Coolant leaks around the thermostat housing or under the vehicle.

On newer vehicles, the check engine light may come on if the vehicle doesn’t reach operating temperature. Likewise, the check engine light can come on when the temperature gets too hot.

If the engine is running hot, one way to test for a bad thermostat is to place your hand on the top radiator hose. If it’s cool, but the engine is hot, it’s likely your thermostat needs to be replaced.

How much does it cost to replace a thermostat?

According to Repair Pal, the average cost to replace a thermostat is between $490 and $525. It could also be more or less depending on the make and model of the car. This cost reflects not only the part but the mechanic’s labor and the cost of coolant and other parts that need to be replaced. Keep in mind that the thermostat is more easily accessible on some cars than others, and the same goes for how easy it is to drain and refill a cooling system properly.

However, replacing your thermostat yourself could cost you less than $50, which covers the cost of the thermostat and coolant.

Can I replace a car thermostat myself?

Absolutely! The thermostat is an easy part to replace. It sits near the top of the engine at the front of the car, so it’s easy to access. It doesn’t have any wires or electronic connections, so it’s an ideal repair for the novice mechanic.

The hardest part is draining the coolant from the radiator. This requires a bucket or drain pan and may require you to raise the front of the car on jack stands. This is also a good time to replace your antifreeze and flush your cooling system.

Here’s a helpful tip: Save your antifreeze jugs to dispose of the old coolant. You will want to take the old coolant back to the auto parts store for proper disposal.

How do I replace my thermostat?

First, you’ll need to gather the following parts and tools:

• Car thermostat
• Coolant – typically two to four gallons depending on your vehicle and if the coolant is concentrated or pre-mixed
• Bucket or drain pan
• Socket wrench or crescent wrenches
• Putty knife or scraper

To change your thermostat, park your vehicle on a level surface, ideally in a garage or

driveway. Then make sure your car’s engine is cool and perform the following steps in order:

1. Remove the radiator cap and then drain the coolant into the drain pan using the radiator drain valve located at the bottom corner of your radiator. To access the drain valve, you may need to raise the front end of the vehicle using a jack and jack stands.
2. Locate the thermostat housing by following the upper radiator hose from the radiator to the engine. The place where the radiator hose connects to the engine should contain the thermostat.
3. Remove the radiator hose from the thermostat housing. This step is not required but may make it easier to remove the thermostat.
4. Remove the thermostat housing bolts with your wrench. Most vehicles have a separate thermostat and thermostat housing, but on some vehicles, the thermostat and housing are integrated.
5. Note the orientation of the old thermostat. You will need to install the new thermostat going in the same direction.
6. Remove the thermostat and gasket. You may need to scrape the old gasket off the engine block and thermostat housing using a putty knife or scrapper. Be sure not to let any pieces of the gasket get inside the engine.
7. Install the new thermostat and thermostat gasket. Make sure it is positioned in the same way as the old one. (The spring side should go into the engine.) Ensure the thermostat sits flat so the housing mounts flush with the engine.
8. Install the bolts to the thermostat housing. Do not over-tighten them. They should be snug and tightened to about 15 lb-feet of torque. If you do not have a torque wrench, tighten the bolts until they are fingertip tight, and then use your wrench to tighten them another 1/4 to 1/2 turn.
9. Reattach the radiator hose and tighten the radiator hose clamp.
10. Lower the vehicle and refill the cooling system with coolant.

Once you have filled the radiator with coolant, leave the radiator cap off and start the car. Let the engine run for about 10 minutes to warm up, checking the temperature gauge periodically. During this time, you will also need to check the coolant level in the radiator and top it off with coolant as needed.

After the car is warmed up and topped off with coolant, reinstall the radiator cap, and you’re good to go.

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