I just bought a 2002 Grand Cherokee with the 4.0, I noticed the engine temperature creeps up too high and then found out the electric radiator fan isn't activating despite the temp climbing well past 210. I was wondering if you guys have any tips on how to determine if the fan is broken or if the fan relay is broken.

 

That's easy! Unplug the fan and hotwire it. It should run on high. In case you don't know where the fan relay is....under the right headlight support panel. The 2002 may have 2 separate relays in the PDC under the hood. If so, the fan will have a 3 prong plug.

To check if it's working right, start with a cold engine, start it up and watch it as it warms up. The fan should kick on high at 210*, run on high until the temp drops to 195*, then run on low until either the temp climbs back up on you shut off the engine. It should run on high whenever the A/C compressor runs.

My WJ fan was cycling properly, but the temp was still staying at about 220* and would creep up to 230* if I was idling for a while in traffic. It turns out the fan was not running fast enough due to having 215K miles on it, so I put a new one in, curing the problem.