4 Wheel Drive/SUVs: electric fan, radiator system, radiator flush

Question
'88 Cherokee 4.0L.
I was driving a rough forest road in 4wd at slow speed. When I parked and shut down, my it started overheating, blowing coolant out of the relief thing on the reservoir bottle.  The temp gauge was near the red arc.  It stayed at normal operating temp when driving home with good airflow across radiator.  I replaced the thermostat, but it didn't help: I left it idling, the temp gauge slowly continued to creep up towards the red.  This is when I noticed the electric fan wasn't coming on.  I hooked the fan directly to power off the battery, and it didn't work, so I got a new fan motor.  It still won't come on.  There also appears to be a crack in the top of the plastic reservoir bottle.
Thanks,
Ross Douglas


Answer
Ross,

Well, the first thing to do, is to replace the reservoir bottle, and the radiator cap.  This will insure that you have the right pressure in the radiator.  Without the proper pressure, usually 13 to15 psi, the radiator will over heat.  As far as the fan goes, you should pick up a repair manual for the Jeep, as it will have the wiring diagrams in it for the fan.  You may have a bad thermostat that is not allowing the fan to function. These manuals can be purchased at most auto parts stores for, around $20.  It sounds like the original fan shorted out, and more than likely blew a fuse somewhere.  A cheap multimeter, or a 12 volt test light can be used to trace out the wiring.  Also, make sure that the new fan has a good ground.  While your at it, it wouldn't hurt to run a good radiator flush through the radiator system to clean out any possible plugged lines.  

Carl