The thermostat in your 1998 Ford 5.4L V8 engine sits near the top of the engine. With the radiator and computer, the thermostat helps control engine operating temperature. After so many cycles though, the thermostat may get stuck open and prevent the engine from reaching operating temperature. Or worse, it may get stuck closed and cause the engine to overheat. Avoid expensive repairs later by replacing a failed thermostat in your Ford 5.4L engine in a matter of minutes now.
Place a drain pan under the radiator toward the drain plug. Open the plug, remove about two quarts of coolant and close the plug.
Disconnect the upper radiator hose from the water outlet at the engine side. Squeeze closed the tabs on the clamp securing the hose to the water outlet using a pair of rib-joint pliers and slide the clamp toward the radiator.
Twist and carefully pull the radiator hose end off the water outlet.
Disconnect the heater water inlet hose and positive crankcase ventilation (PVC) hose from the water outlet as well, if your 5.4L engine comes with them. Use the pair of rib-joint pliers and a flat-head screwdriver if necessary.
Unfasten the power steering reservoir bracket and move the reservoir to the side if you need better access to the water outlet. Use a ratchet, ratchet extension and socket.
Unfasten the two water-outlet mounting bolts using a ratchet, ratchet extension and socket. Lift the water outlet off its engine-mounting base.
Look at the mounting position of the thermostat so you will install the new thermostat in the same position. Remove the thermostat and O-ring seal from the engine-mounting base.
Position the new thermostat and new O-ring seal in their engine-mounting base. Double-check the thermostat spring points toward the engine, and the pointed end toward the radiator hose, says James E. Duffy in “Modern Automotive Technology.”
Seat the water outlet on the engine-mounting base and over the new thermostat. Thread the water-outlet mounting bolts finger-tight. Tighten the bolts to 18 foot-pounds (25 Nm) with a torque wrench, ratchet extension and socket.
Install the power steering reservoir bracket with the ratchet, ratchet extension and socket.
Connect the heater water inlet hose and positive crankcase ventilation (PVC) hose to the water outlet, if your 5.4L engine comes with them. Use the pair of rib-joint pliers and the flat-head screwdriver if necessary.
Attach the upper radiator hose to the water outlet.
Squeeze the tabs on the clamp of the upper radiator hose with the pair of rib-joint pliers and slide the clamp over the end of the hose to secure it to the water outlet.
Refill the cooling system with a new mixture of antifreeze and distilled water as necessary to replace the drained coolant.
