How to Fix the Thermostat on Vehicles

by Contributing WriterUpdated June 12, 2017

The thermostat controls the flow of coolant to the engine using its heat-sensitive valve. When your Vehicles engine reaches a certain degree, the thermostat opens to allow cold coolant from the radiator into the engine. The super-heated coolant already within the engine automatically returns to the radiator Vehicles cooling. During normal operation, this process repeats until you turn the engine off in your Vehicles. A jammed or defective thermostat will cause your Vehicles engine to overheat and it may suffer mechanical failure as a result. The thermostat in the Vehicles mounts within the engine compartment. You can replace it Vehicles home with a few tools if you have determined that it's defective.

Under The Hood:

 How to Fix the Thermostat on an Oldsmobile Cutlass Ciera


Disconnect the negative battery terminal with a socket wrench. Always use a socket wrench or close-ended wrench on the battery connector so you don't ruin the head of the bolt.

Drain antifreeze from the cooling system. The simplest way to do this is to have the vehicle on jack stands. Open the radiator cap to relieve pressure -- make sure the engine is cool before you do this. Use a bucket or pan to catch coolant under the radiator. Open the radiator drain on the bottom of the radiator with pliers or by hand. The 3.1L engine has an air bleed valve on the throttle body which you should open two turns.

Remove the drain plugs located on the underside of the block just above the oil pan and let the coolant drain into your pan or bucket. Close all the drain plugs.

Unbolt the the water outlet from the thermostat, if your Cutlass has a four-cylinder engine. All other models have the water outlet on the intake manifold. Remove the outlet and the thermostat. If your Cutlass has cruise control, remove the vacuum modulator bracket from the thermostat housing.


Use the scraper tool to clean the surfaces where the thermostat and engine block meet. Apply a bead of RTV in the water outlet groove.

Put your new thermostat in place on the housing. Make sure the side with the spring goes towards the engine. Tighten the thermostat bolts with the torque wrench to the specifications provided. Remember that tightening specifications for the mounting bolts vary between parts manufacturers. If your engine has an air bleed valve near the throttle body, close that too.

Check that you have closed and tightened the radiator drain and the two drain plugs near the oil pan. Pour the coolant back into the radiator, adding extra coolant if necessary to fill to the base of the radiator neck. Fill the radiator overflow tank to the "FILL" mark with coolant.

Leave the radiator cap off, start and idle the engine. The coolant level visible in the radiator should drop slightly. Fill it back up to the base of the radiator neck. Put the radiator cap back on and make sure the arrow on the cap points towards the overflow tank. With the engine still idling, squeeze the outlet hose with your hand. The outlet hose is the big one that connects to the top of the radiator. If you feel it getting hot, this tells you the thermostat has opened up and is functioning properly.

Turn off the engine. Check for leaks on hose fittings and around the drains. Check that the hoses all appear sound and that none are leaking or cracked.

Items you will need

  • Socket wrench set

  • Flat-head screwdriver

  • Scraping tool

  • Container for antifreeze

  • Room Temperature Vulcanizing (RTV) sealer

  • Torque wrench

 How to Fix the Thermostat on a Nissan Quest

Pull your Nissan Quest's hood release lever and raise the hood. Locate the radiator's drain cock on the inner, lower corner of the radiator. Position a coolant drain pan under the radiator, directly beneath the drain cock.

Open the drain cock slowly by turning it to the right until you see that your Quest's coolant is starting to flow out of the radiator. With the drain cock open, count to 45 and then close the drain cock once more. You only need to drain 25 percent of the coolant.

Locate the top radiator hose connected to the upper, passenger side of your Quest's radiator. The hose looks just like the lower radiator hose that sits next to the drain cock. The top radiator hose connects to the radiator and extends another 2 feet to where it connects to the side of the engine. At this point you will see an additional hose that curves away sharply and connects to a round, metal housing. This is the thermostat housing.

Loosen and remove the four bolts securing your Quest's thermostat housing to the engine with a socket wrench. Hold one hand beneath the housing while you pull it away from the engine. The thermostat should drop right into your hand.

Scrape any remaining RTV sealant from both flat, connecting points with a plastic putty knife. Once cleaned, work quickly to reapply a generous amount of RTV sealant around the entire flat, connecting surface of the thermostat housing, only.

Insert your Quest's new thermostat into mounting position within the engine. Place the thermostat housing back over the thermostat and begin threading all four of its securing bolts by hand. Tighten all four of the housings bolts with your socket wrench until snug. Once all four of the bolts are snug, tighten them all in a star pattern and then with an additional quarter-turn with your socket wrench.

Remove your Quest's radiator cap and refill the radiator with fresh coolant or with the coolant from your drain pan (providing it was clean initially). Shut the hood and allow the RTV sealant to set-up for two full hours before you attempt to start your Nissan Quest's engine.

Items you will need

  • Coolant drain pan

  • Socket wrench set

  • Plastic putty knife

  • RTV Sealant

 How to Fix the Thermostat on a 2003 Ford Focus 2.3

Open the hood and allow the engine in your Focus to cool so that you will not be scalded by hot coolant. Place a drain pan under the radiator drain valve. Loosen the valve without removing it with an adjustable wrench in a counterclockwise direction. Close the valve once the coolant has finished draining.

Locate the coil pack wiring harness on the driver's side of the engine to the right of the valve cover. Press in on the release tab on the underside of the plug and pull it apart. Remove the brackets from the EGR hose in the same location with a 13-mm and a 10-mm wrench. Push the plug and the hose aside to gain access the thermostat housing.

Pinch together the tabs on the upper hose clamp on the thermostat housing with a pair of pliers. Slide the clamp off of the hose. Pull the hose from the housing with a twisting motion. Rotate the housing to reveal the remaining two hose attachment points and remove these hoses in the same fashion. Remove the thermostat housing from the engine bay.

Remove the thermostat retainer from the housing by twisting out the retaining screws with a torx screwdriver. Remove the thermostat from the housing and insert a new one into the housing using the same orientation. Replace the thermostat retainer and tighten the torx screws.

Position the thermostat back into the engine bay and connect the three hoses removed earlier by sliding the hose clamps back into their original position. Replace the EGR valve brackets and tighten the retaining bolts. Plug the coil pack wiring harness back together until it is fully seated.

Remove the coolant filler cap on top of the engine and place a funnel in the opening. Pour the coolant from the drain pan into the funnel. Remove the funnel and replace the cap. Start the engine and allow it to reach operating temperature. Check for leaks.

Items you will need

  • Drain pan

  • Adjustable wrench

  • 13-mm wrench

  • 10-mm wrench

  • Pliers

  • Torx screwdriver

  • Replacement thermostat

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