Cooling problem....
 

88 Cherokee Laredo 4x4 keeps overheating. Replaced cracked coolant resevoir and clutch fan. A/C aux fan comes on when A/C is turned on but has never come on when temp gets hot. It slowly climbs past 220 then I shut her off. Could it be the temp sensor in the rad ? Any way to test the sensor?

I have a 88 like yours and have come through all this sht before.
The aux cooling fan should come on also when the temperature gets over a certain value. If it doesen't, change the temp sensor in the rad.
I would strongly recommend u to unweld ur radiator and have it clean inside. U don't imagine the amount of dirt that 21 years of service can bring to it.
Upgrade to twin audi a4 or a6 electric fans, they pull the asphalt through that grill...

ah, forgot, u can test the sensor for continuity (the buzzer on the voltmeter) when it's really hot, should buzz.

where does one get these aux fans? mine's very loud and on the verge of dying i think. i want to replace it and why not replace it with something better!

scrapyard, dude...

If you do not have a multimeter, you canunplug the sensor from the radiator and jump the plug that plugs into the sensor and the fan should turn on....(been there, done that..)

I have a similar problem. I just replaced my t-stat, my elec. fan has juice going to it, spins freely w/no resistance, but doesn't kick on. What gives? It was 85 today and it was hitting 220 on the gauge but no elec. fan kicked on ever. I'm moving to Texas in 3 mos, is this thing gonna melt? FRUSTRATED:gun_bandana:

This is what I have instead of the crappy stock fans:
Audi A6 twin fans with curved blades and bypass switch to run them continuously.

Ok, replaced the coolant temp sensor in the radiator, fan still will not turn on when it gets hot, ie- over 220. Fan does work when jumpered or A/C is turned on. Any suggestions?

Ok, no panic, what are u exactly jumpering?
U should jumper the temp. sensor connector (ign. ON) to see if the wires are ok.
The fan should come on, if it doesen't check positive feed on YELLOW wire of the connector with tester, with ignition on. U should have 12volts. If not follow cable and find interruption.
If u have 12v instead, means that interruption is on the GRAY wire between the connector and the fan diode assembly (not the fan relay) positioned under the LH hood latch. This diode has three wires, two ORANGE and one GREY.
Orange A: +12V coming from the AC
Orange B: +12V going to the fan relay
Grey C: +12V coming from the temp sensor if working (temp over 190)
This diode works so that current can flow only in one direction (orange B) and not backways in A and C.
From there on everything should be ok, cause ac on=fan on.
If all the wires are ok it means one out of 2 things:
-temp sensor is good and radiator doesen't get hot enough due to stuck thermostat or big air bubble.
-temp sensor is not good. :detective:

Really putting your ele fan on a switch I have found to be great. You can run the fan whenever you want without the ac being on. I can keep my truck under 200 even when sitting or wheeling just by using the stock ele fan. If you wanna upgrade to dual ele fans that would be even better.

I like this idea!! Which year a6 twin fan fits best? My dad is away and I'm fixing up the 90 xj that has 80,000 miles. I've begun searching the reading all about the cooling problems and fixes I replaced both the grommets on the value cover since they were torn open, I still need the 2nd half of the Vacuum Harness(5300-4838) anyone have the part#?? The grommets helped but not completely (220ish) - before it pushing the redline.

Just changed t-stat (oem 195) and flushed the radiator, no particular sequence though. Had issues but tried the technics mentioned here to get the air out. Ran the jeep for about 15 mins with cap off... check the aux fan, work with a/c only. I kept doing this, let run to long or gave it throttle and overflowed when i shut off. Did a few more times, capped it and test drive was right at 195, maybe 210 at a stoplight, now much better. The temp did bounce up and down, radiator has never been flushed/cleaned so i think its clogged or the water pump is having issues??

off the bat I know i want the a6 twin fan and to clean the radiator (you say it has to be unwelded?). Maybe change the belt, replace water pump and I'd like to remove the a/c, can i replace the a/c with a idle pulley? The motor itself needs some attention too, other then valve cover gasket, plugs and wires, thats all that been done. This has all original hoses, cars has started everything time so im guessing it can't be in horrible condition. I Just know my dad doesn't maintain the car.

anyhow, first post here and love all the tech information and boards. I'm really enjoying working on these xj and they seem to be built solid which was not how i thought they were.

Basically 1990 Audi 100 to 1996 A6 will be good. The good thing is that the fans are one piece with the housing. I just cutted the housing all around and screwed it to the frame. Very easy.
The vacuum grommets on the valve cover have nothing to do with cooling issues. These are for crankcase ventilation.
Your auxiliary fan should come on when the temperature rises over 89°C (192°F), that's what the temp sensor on the rad is for.
If the water pump turns and does not leak it is ok.
The belt is to be changed if it starts to crack.
U can swap the ac compressor, i would put a volumetric supercharger instead.
I cleaned my radiator my self, to save some money but u can bring it to the radiatorist to have it clean for about 75$

You can use a switch, but that switch should run your relay. If you use a switch to run it directly, it will eventually fry.