How to change your vehicle's thermostat

A thermostat regulates your engine's operating temperature. If your car, truck or SUV has been overheating, running hot or isn't producing much heat, it's a good indication that you may need to replace it's thermostat. Replacing thermostats on modern vehicles with their crowded engine compartments can appear intimidating at first, but don't sweat it, changing thermostats on most vehicles is easy, and cheap. On most vehicles it is a half-hour project.

While thermostat locations differ between types of vehicles, the process of replacing a thermostat is generally the same for most vehicles. Follow along as we change a thermostat on a vehicle with a very crowded engine compartment.

What you need:

Wrenches & 3/8" socket set (metric  Clean drain pan    or SAE depending on vehicle)  Pliers  Screwdrivers  New Thermostat & Gasket  Grease rag  Gasket Scraper or Razor

Procedure:

1. Drain Radiator
Begin by draining about a gallon of antifreeze out of the radiator. Loosen the drain petcock located on the bottom of the radiator. You may be able to reach the petcock from the top of the engine compartment, if not, you may need to raise the vehicle slightly with a jack to access it from below. After draining antifreeze, be sure the drain petcock is securely tightened.

2. Locate thermostat housing
On most vehicles, the thermostat housing is the metal piece on the engine that the upper radiator hose attaches to. The thermostat will be beneath the housing. If your engine compartment is packed tight with accessories like ours is, you may need to unbolt and remove the air filter box like we did to get better access to the radiator hose and thermostat housing. Most air boxes are easily removed with a couple bolts and hose clamps. See Large image of engine compartment

3. Remove radiator hose
Remove the end of the upper radiator hose that attaches to the engine. On most vehicles, the hose is held in place with either a heavy-duty spring-type clamp or a screw-type hose clamp. Screw-type hose clamps can be removed with a screwdriver (some penetrating fluid on the threads helps). Spring-type hose clamps like our vehicle has can be pinched together with a pliers and wiggled either towards the engine, or towards the center of the hose. Once the clamp is removed, wiggle the hose side-to-side to unseat it from the thermostat housing. If the hose is difficult to remove (which they usually are) gently pry under the end of the hose with a screwdriver. Be careful you don't damage the hose. Typically, you don't need to remove the entire radiator hose, just the end near the motor.

4. Remove thermostat housing
The thermostat housing on most vehicles is the metal piece on the engine that the upper radiator hose attaches to. It is typically held in place with a couple of bolts. Remove the bolts and remove the housing. The thermostat housing may be stuck to the engine via a gasket and may require some gentle prying with a screwdriver to remove it. Our vehicle used a rubber gasket instead of a paper gasket so it removed easily and little cleanup was necessary. Once removed, some antifreeze may spill out.

5. Remove thermostat
With the housing removed, the thermostat should be visible and should easily pull out. Before you remove it, however, note which end of the thermostat protrudes from the engine. The new thermostat must be installed the same way.

6. Remove old gasket material
If necessary, use a razor blade or gasket scraper to thoroughly remove ALL old gasket material and any corrosion from the thermostat housing and the engine. Use care if either are made of aluminum as it is easily nicked-up with a razor blade. Finally, wipe surfaces clean and dry with a grease rag or paper towel. Use solvent such as paint thinner, if needed, to remove any grease or oil.

7. Install new thermostat and gasket
Install new thermostat and gasket. On most engines, the thermostat fits into a special recessed ring. Take care that the new thermostat is installed correctly with the proper side towards the engine (spring side usually toward engine). Then, install the new gasket.

8. Reinstall thermostat housing
Carefully position the thermostat housing in place. Take special care that the thermostat doesn't accidentally move out of it's seat upon installation. If the thermostat is not properly seated, it could cause the housing to warp or crack when bolted in place. Once you are sure everything is positioned correctly, bolt snugly into place.

9. Reattach hose
Reconnect the upper radiator hose and hose replace clamps. Inspect the hose. If it appears to be flimsy and enlarged near the clamp area, it is weak and now would be a good time to replace it.

10. Refill radiator
Pour as much antifreeze as you can back into the radiator and tighten the radiator cap. The entire drained portion may not all fit in so either pour the leftover into the overflow tank or add later after the vehicle has been tested for leaks and allowed to cool.

11. Check for leaks
Run vehicle until fully warm and check for leaks. Specifically, check the gasket and hose at the thermostat housing, and that the drain petcock is securely tightened. We ran our vehicle around the block a couple of times and afterwards everything appeared nice and dry.

12. Recheck coolant level
After vehicle has cooled sufficiently, check coolant level again. Add a 50/50 mix of coolant and water as necessary.