How to Change the Thermostat on a 1998 F-150

by Lisa Wampler

Your 1998 Ford F-150 has likely lived a life of hard work and hard play but the Ford F-150 was designed to be the workhorse of the truck market. If the cooling system is not properly maintained it can reach an early grave. When the thermostat stops working it can mean an engine melt down for your Ford. The engine can overheat and warp the engine heads or even the engine block. When this happens the repair bill will cost more than the vehicle is worth. This makes changing a part that only costs a few dollars a great investment in your F150's future.

Remove the bolts that hold the thermostat intake cover onto the intake manifold of the F-150 with an adjustable wrench. Place the bolts off to the side. They will be reused during the installation process. Pull the radiator hose the thermostat cover is connected to into the air and let the antifreeze flow back into the radiator.

Pull the thermostat out of the exposed hole in the intake manifold with your fingers. The thermostat is not bolted into place. It sits on a machined flange inside of the intake manifold.

Pull the old carbon thermostat gasket off of the intake manifold and discard it. Place a bead of RTV silicone on each side of the new thermostat and place it onto the intake manifold. Make sure to line the holes cut out of the gasket for the bolts up with the actual bolt holes on the intake manifold.

Place the new thermostat back into the intake manifold with the correct end facing out of the engine. The end will be marked as the top of the thermostat.

Place the thermostat cover back onto the intake manifold and bolt it into place. Start the engine and check for leaks. If you see any leaks tighten the cover down to remove them.

Items you will need

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  • photo_camera radiator humor image by John Sfondilias from