If an engine overheats, the damage can ruin the engine by cracking the head or causing the pistons to seize. As soon as there is a noticeable level of excessive heat or no temperature reading at all, it is time to find out what is wrong. If the thermostat and temperature gauge have been eliminated as possible sources of the problem, then you need to replace the fan relay. The fan relay transmits the temperature information from your Jeep Cherokee's thermostat in order to turn on the cooling fan when needed.
Use a flat head screwdriver to pop the plastic covers off the plastic rivets holding the assembly in place at the wheel wheels.
Nip the top of the plastic rivets off with a pair of side-cutting pliers. Push the remainder of the rivets out of place with a Phillips head screwdriver.
Remove the upper bolt holding the assembly (fascia or bumper and frame) to the wheel wells with a 10 mm socket and socket wrench. There is one bolt at each wheel well.
Open the hood and remove the four screws along the top of the grille/fascia assembly with a 7 mm socket and socket wrench.
Pry out the three plastic push-pins from the bottom of the fascia that hold it to the frame along the front edge of the Jeep with the flat head screwdriver.
Use the 7 mm socket and socket wrench to remove the three screws holding the front of the assembly onto the frame. There will be one screw in each corner of the grille area and a third screw placed off-center in the grille area, along the bumper edge and towards the passenger's side of the Jeep.
Unplug and remove the fog light sockets from the assembly. Push the sockets in and rotate them 1/4-turn counterclockwise then pull the socket from the assembly.
Pull the entire grille and fascia assembly off the frame of the Jeep.
Disconnect the negative cable from the battery by loosening the locking nut and pulling the cable off the battery terminal.
Remove the top support bolt from the coolant reservoir at the front, passenger's side of the engine compartment with the 7 mm socket and socket wrench.
Unscrew the two bolts that mount the reservoir to the front of the Jeep's frame with the 7 mm socket and socket wrench. Lift out the reservoir and set it aside.
Disconnect the vacuum hose from the bottom of the reservoir. Use the Phillips head screwdriver to loosen the locking collar then pull it out of the fitting. Push the vacuum hose out of the way.
Remove the two relay mounting bolts with the 7 mm socket and socket wrench. Grab the relay housing and pull it out of the engine compartment far enough to access the wire connector.
Disconnect the relay by pressing the tabs in on the side of the connecting plug and separating the relay from the engine's electrical harness. Remove the relay and discard it.
Connect the new relay by pushing the two halves of the connector plug together (one from the relay and one from the engine's electrical harness).
Mount the relay onto the frame by pushing the relay mounting bolts through the housing and into the frame then tightening each bolt 1/2-turn past hand-tight with the 7 mm socket and socket wrench.
Reconnect the vacuum hose and return the reservoir to its place in the engine compartment. Make sure to place the two mounting bolts first before the top supporting bolt is installed for the reservoir.
Remount the grille/fascia assembly by pushing it into place and reinstalling all the bolts and screws needed. Make sure to add plastic panel plugs at the wheel well to replace the plastic rivets that were cut off during the removal process.
Reconnect the negative battery cable to the battery.
