The 3.8L Mustang is one of the smallest motors that Ford has used in the Mustang. A side effect of a small engine in a sports car is premature breakdown of mechanical parts like the thermostat. Driving an engine hard can cause strain on engine parts. When the thermostat stops working, it can leave your Mustang sitting by the side of the road waiting for a tow truck. Replacing a broken thermostat will help to extend the life of your Mustang.
Remove the radiator hose from the thermostat housing by loosening the band clamp that holds the hose onto the housing. Use a flathead screwdriver or a nut driver. Pull the hose off of the housing, and drain any excess fluid trapped in the radiator hose into a bucket.
Take out the two bolts that hold the thermostat housing onto the intake manifold of the Mustang with a wrench, and pull the housing off of the manifold.
Pull the thermostat out of the intake manifold, and remove the paper gasket that sits on top of the machine base of the intake manifold.
Place a new paper gasket onto the machine surface of the intake manifold, and place the new thermostat back into place. The end that must stick out of the engine is marked "top."
Put the thermostat housing back onto the intake manifold, and bolt it back into place. Reattach the radiator hose, and tighten it down.
Start the engine, and let it warm up. Check the mating surface of the intake manifold and the thermostat cover for any leaking. If there are leaks, place RTV silicone on each side of the thermostat gasket to prevent future leaks.
