i have a 00 cherokee sport 4.0. the wife usually drives it to work, today she in a drive through line she said the coolant temp gauge pegged to hot rather quickly. she pulled into a parking spot and shut it down. then it wouldnt start.
she called, i suspected vapor lock, so i had her open the hood and wait a few, then all was well, until she started driving it, then the overheating started again.

i have a switch to turn on the 10 blade efan, i also have an aftermarket 900 cfm pusher efan installed on the other side of the radiator, both of which were on, and still the temp gauge reads to the mark PAST 210.

today i replaced the thermostat. no change. after replacing the thermostat, i flushed the heater core with a garden hose, because the winter we never really had "hot" heat.

what's next?

 

When my 01 started over heating I needed a water pump. not sure if that's common on these years or not. but mines been fine ever since.

 

00 and 01 are prone to cracked heads. Check for coolant in oil and oil in coolant. Check compression with a Gauge and/or leak down test make sure it's good. If the radiator is original replace it. Mechanical fan clutch, water pump, thermostat. Just check all of it. Replace any Colin system components that are questionable. Honestly not that hard or expensive to do it all in one go.

 

Funny you say that, Ive replaced my cylinder head and my radiator too. but its all worth it to not have coolant in my oil. she runs good now besides the damn oil pressure wont stay up. probably a faulty gauge.

 

mopar water pump on order. and high flow tstat with bleed (jiggle) valve. i argued with the counter guy at o'douche's that our engine's thermostat didn't need the jiggle valve....smh.

 

maybe the damage was done to the bearings before you caught it. If the bearing clearances are too much it will result in low oil pressure.

 

OP, the head on your 4.0 is likely cracked and beyond repair.

 

First thing to check on this model year.

 

Indeed. You can throw all the thermostats and radiators, change all the fluids all you want to on the 00-01s. It won't stop the overheating. They have a know casting flaw between #3 and #4 valve pocket that causes the head to crack there on the original non-TUPY 0331 head.

 

I've done 5 head swaps now, and all resulted in the gauge reading lower than before. 4 were preventive and only 1 was because of a crack. I think it's a dummy gauge and for whatever reason replacing all the c**p involved in a. Head swap somehow makes it read actual pressure haha.

But on the one with the crack, it was prob bearing wear, nothing Delo diesel oil couldn't fix haha.

 

one thing i failed to mention, when it was overheating the first time in the drive through line, coolant was pouring out of the stem and cap of the overflow tank.

today i flushed the radiator and did a compression test. 170 psi all cylinders.

 

also i failed to mention, today when i filled up the radiator (water only) i started the engine with the cap off and slowly the water began to pour out of the fill hole in the radiator. it kept doing it and getting worse until the thermostat opened, but that didn't really stop the temp from rising. it got up to about half way between the 210 mark and the next mark. the efan kicked on, and just stopped the temp from climbing, but didn't cool it down.

also, i have a zj hd fan clutch on it.

 

I have heard you can get a kit to check for combustion gasses in the coolant. Some have also said they have sent theirs off for an analysis.

I believe compression specs are 120-150 PSI for the 4.0, with no more than 30 PSI variation between cylinders. I would be surprised if you had no variation at all between cylinders, as you reported.

If you haven't done a leak-down test, you might consider it.

 

I've used Amalgatech for coolant contamination analysis.. it's pricey, but it can tell you a lot about what's in your coolant.

Call Ed Eaton. He's an industry expert..

http://www.amalgatech.com

.

 

You need to investigate your cooling & oil systems.
The first thing I would do is remove the valve cover to visually inspect the head.