The thermostat in your Ford 4.0 liter engine is necessary to the operation of your engine's cooling system. If you have noticed that your engine is running hot or, that the temperature gauge does not seem to be reading correctly then you need to replace the thermostat. You can install a thermostat in a Ford 4.0 liter engine (the engine used in almost every V6 Ford truck and car) in about an hour.
Park your car or truck on a level surface. Wait for the engine to completely cool. Open the hood and remove the radiator filler cap (this unscrews by hand).
Place a bucket under the vehicle beneath the driver's side of the radiator. Reach under the radiator and turn the drain petcock towards the front of the car. If you have difficulty turning the petcock by hand, clamp a pair of vise grips to it and turn it using those as a handle. Allow enough coolant to drain out of the radiator so that you can see the top of the metal fins inside the radiator when you look in through the open fill cap. Close the petcock.
Trace the coolant delivery hose from where it comes off radiator to where it joins the thermostat housing. The thermostat housing will be located on the top of the engine block, toward the front. It is metal and the delivery hose will feed into it and there will be two additional hose coming off the housing.
Loosen the hose clamps attaching the hoses to the thermostat housing by turning the hose clamp screws counter-clockwise with a flat head screwdriver. When the clamps are loose enough to spin around the hose, pull the hoses off the housing.
Remove the four bolts holding the housing cover in place with a socket wrench. Lift the housing cover off. Inspect the gasket underneath the housing, replace it if it is brittle to the touch or looks worn. Scrape off the old gasket with a paint scraper put a new one in its place.
Remove the old thermostat from its position in the housing by simply lifting it out.
Install the thermostat into your Ford 4.0 liter by placing it in the same position as the old. Make sure that the silver top is facing upward and the arrows on the top are pointed toward the radiator.
Replace the thermostat housing cover and bolt it into position. Re-attach the hoses and tighten the hose clamps. Fill the radiator with new coolant and replace the filler cap.
