How to Change the Thermostat in a 1998 Ford Explorer

The engine coolant thermostat acts as a gateway in the cooling system to allow or disallow the passage of engine coolant through the engine. To run optimally, the engine on your Ford Explorer needs to maintain a constant temperature, give or take 10 degrees. The thermostat closes when the engine temperature drops below that threshold and opens when it rises above it. Unfortunately, thermostats are not made to last forever and should be replaced during every cooling system repair. Make sure the engine is cold before beginning any cooling system work.

Place the drain pan beneath the engine, below the thermostat housing. Locate the thermostat housing by following the upper radiator hose from the radiator to the housing.

Use the socket set to loosen the hose clamp on the upper radiator hose and then pull the hose off the thermostat housing by hand. Aim the hose down toward the drip pan to catch any coolant that may escape.

Use the socket set to remove the two bolts that hold the thermostat housing to the top of the engine. Lift the housing off by hand. Inspect it to make sure it has no signs of corrosion; set it aside. If there is any corrosion, you will need to replace the housing.

Pull the thermostat out of the well in the top of the engine. If it is stuck, you can use the pocket screwdriver to lift it out. Either way, it should come out easily. Note how the thermostat was positioned and oriented in the well for reference during installation.

Install the new O-ring seal around the base of the new thermostat, if it is not already present. (Some come attached in the packaging while others have the O-ring loose in the bag the thermostat is sold in.) Make sure it is properly seated on the thermostat flange. Compare it to the old thermostat for reference. The thermostat on your Ford Explorer does not have a gasket as the O-ring performs the same function, so there is no need for adhesive.

Place the new thermostat in the well, with the spring facing down into the engine. Make sure it is seated correctly. Reinstall the thermostat housing and upper radiator hose in reverse of how they were removed. If you lost any coolant in Step 2, replace it now with a 50/50 mixture of coolant and distilled water.