algebraic429

1993 Cherokee XJ 200k miles with 4.0six and automatic. 6.5 inch lift with 33” tires on stock gearing 3.55, with ac on in traffic or idling the temps creep past 210 and then just keep going. I dont get steam or anything and ive never let it go past the second white line on the gauge. but once it heats up like this it wont cool back down to 210 even if i turn the ac off and im moving on the freeway. It will cool down a little but stays hot. Without the ac on the temps will stay at 210 in all conditions maybe creep a little past 210.

Previous owner for unknown reasons overhauled the cooling system and AC system

these are the parts Previous owner replaced, New water pump, hoses, 180f thermostat, new 4 row aluminum radiator from Amazon. New stock fan clutch. New Efan from a later model XJ.converted ac system to r134 and new condenser

When I bought this jeep I test drove it and with the ac on and everything is fine but I didn’t drive it that long. I also noticed after I bought it looked like the guy was running straight water for who knows how long

After owning it for a few months and getting into the summer months I noticed it getting hot with the AC on at idle or very slow speeds. It takes awhile but the temp will just keep creeping up and even if I turn off ac and keep driving it drops a little but won’t get back down to 210

I went on deep dive of research and then started replacing stuff as I went.

What I’ve done so far
Drained and replaced coolant a few times and then also did prestone chemical flush. There was small specs of rust in coolant before the flush but it looked pretty clean. Upon removing the old (new) aluminum radiator I heard a noise when shaking the radiator and upon inspecting the inside I noticed huge chunks of what I think is rust.

The parts I’ve replaced so far, New oem style radiator. 195f thermostat, ZJ fan clutch, new hoses, water pump, aux trans cooler.

It doesn’t lose coolant, oil doesn’t look milky. When I burp the system the typical bubbles come out but then stops.

I’m thinking of trying another cooling system flush but this time using a more serious chemical flush like thermocure and also doing a real flush with a garden hose attached. To this point I’ve only drained and filled

I’m also thinking maybe the stock gearing with oversized tires is causing this? People seem split on this though.

pictures are just what i saw when doing the new radiator and what i pulled out of the old radiator. Also an inside picture of the large chunks in the old (new) radiator and a picture of the old (new) water pump

IJM

That pic behind the water pump doesn't look bad, but I'd be willing to bet you've got a bunch of rust inside the water jacket and the radiator that's blocking flow and acting as an insulator. Definitely give it hell with the garden hose, particularly where both heater hoses enter and exit the engine, as they'll bypass the thermostat and allow you to flush the block fairly well. Also, flush out the radiator, and don't forget about the heater core. Once you're done with that, run some Thermocure through the system, and then flush it again. When doing the final coolant refill, I like to add some extra coolant to the mix since there's likely to be some water that doesn't drain out.

Oh, and be sure to use distilled water for your coolant mix.

algebraic429

i pulled the theromostat out and got some pictures of the inside, i also took off my coolant reservoir and cleaned it out. Rust colored sludge on the bottom was very thick it probably filled the bottom 1" to 2" of the tank. I have CRC thermocure, im going to flush the engine with it this weekend

robsjeep

Your gearing is much to wrong for the tires you have, at slow road speed you will need to down shift to first gear (get a 1/2 override switch installed so you can select 1st or 2nd) even so this may not be enough increase in engine speed to keep you water pump and engine driven fan going fast enough. You should regear, 4.56 gears are better for 33 tires.

flush the coolant system, yes a hose flush is good, follow instructions for the coolant cleaners, dont leave them in the system too long, as that can ruin components, cause leaks

make sure the belt is not slipping, assure it is routed correct. make sure you have a fan shroud.
amke sure the "amazon" radiator is of good quality and is a thick one. some amazon stuff is junk. Summit sells a very nice thick all cooper/brass radiator. That is what I gots.

Soemtimes you may simply have to turnt he AC off during rock crawls, as you are at low road speed, so there is little ram air and the engine is working hard, specially with your gear and wheel combo, which is horridly wrong. YOU SHOULD REGEAR.

bluejeep2001

Besides the lots of rust, does the aux cooling fan come on at * 220* ish. Does it come on when the ac clutch engages?

algebraic429

I plan on re-gearing but having read every single possible cherokee overheating forum thread and facebook group post i was seeing a lot of debate on how much impact oversized tires on stock gearing would have on the overall cooling system. But i agree with the logic that bigger tires and stock gearing is gunna make the engine work harder. I have a fan shroud and i already replaced the amazon radiator with the basic autozone one which looks exactly like the spectra premium.

to be clear this thread was a last resort kinda thing, i tried doing my due diligence and read as much as i could before i made a post. I am reserved that if at the end of the day i cant run the AC in traffic or on the trails on hot days then its fine ill live.

algebraic429

yes aux fan runs with ac, and i have a switch to turn it on when i want.

PJB

Make sure you clean out that overflow tank really well, you should see nothing but plastic

algebraic429

If the bottom of the overflow becomes clogged can this have an impact on the cooling system? I thought overflow was only for when it overheats.

bluejeep2001

On the open cooling such as yours..as coolant gets warm/ hot and expands and raises the level in the overflow tank. When it cools it sucks from overflow tank to refill radiator. If coolant tank is blocked with sludge, its easier to pump in under pressure than suck out under vacuum. Several cycles of this and your tank is high and the radiator is low.

algebraic429

I ran the thermocure, when I was burbing the system the distilled water started to come out really dark like this. I drove it today to work and then tonight I’ll drain it and flush it


edit: after doing research its normal for thermocure to turn this color and for it to stink really bad.

slant six

I had a similar problem on my '96 Stock XJ with a 4.0 - I bought a nice Mishimoto $500 Radiatior It helped a bit but still was warm.

I found the Thermostatic fan clutch was the real problem. When I bought a new one and replaced it my problems went away and it became a lot cooler to drive when using A/C and in slow traffic.

algebraic429

Ive replaced fan clutch twice, first time with stock oem one and this last time with ZJ. Ive done as much research on you can about radiators for the XJ and i came away more confused than before. A lot of people swear by the stock OEM style rad which is what i recently installed but i see some people swear that an upgraded all metal, two or three core radiator with decent interior tube sizes is whats best. My jeep mechanic with 30 years experience says the absolute best in his opinion is the OEM mopar heavy duty 2 row that was for the towing package but i cant seem to find one. I was also having trouble finding a new one from a different brand that was as close as possible to that mopar HD rad because the dimensions of the internal row and radiator itself are hard to find to compare.

Very Red XJ

A lot of cooling problems can be solved by venting the hood with louvers or spacers on the rear hinges raising the back of the hood up to let the heat out . REGEAR the diffs or you will end up rebuilding them

algebraic429

I have the hood risers but I’m considering doing the vents. Drove it to work today it was running hot even without the AC it is 100+ and I’m in traffic. I noticed when I got home I have coolant leaking from the housing right before the transmission belly pan but I can’t find a source. The overflow outlet looks dry up in the engine bay and none of the houses look to be leaking