Weird overheating issue. Mechanics couldn't figure it out...

Sorry for the novel, but I want to be through in my explanation:

Took 98 XJ to mechanic 2 weeks ago for brake work and overheating issues. Mechanics had my vehicle for a week, said they couldn't figure out the overheating issue. They said electric fan was bad and need replaced and it needed flushed. So they replaced the fan and did a flush. It was still getting hot.

In their guesswork they also replaced my radiator, and water pump (which I ended up not paying for). They said with a infrared thermometer it was showing to only be hot right in front of the water pump. Said It was drivable as long as I wasn't going to long trips. They said the head gasket was fine. I don't have any symptoms of a blown gasket as far as I can tell. So since I just needed transportatoin for the 10 miles to work, I picked her up and have been driving her sparingly.

I noticed the coolant was rusty again, so I decided to clean it myself in hopes that it just had too much crap in it.

So I began my journey:

I pulled the inlet/outlet hose on heater core and did a flush the other day, (got all kinds of black stuff out of it) in preparation for a full system flush.
Yesterday I spent 6 hours flushing the coolant system myself. Bought the Prestone flush and fill kit.

Here is what I did:

Flushed with garden hose til water came out clear, then started jeep let it run til the water came out clear.

Drained from lower hose, and filled with 2 bottles of Prestone Radiator flush+cleaner. Topped it off with distilled water. Drove 20 miles, and let it run in driveway for an hour.

Flushed again with garden hose til water came out clear, then started it to clean the block, and let it run til water came out clear again.

Drained from lower hose, filled with distilled, let it run for 10 minutes, drained, filled with distilled, let it run for 10 minutes, drained from lower hose, filled with distilled, and let ir run, then let it sit for the night.

This morning came out drained it again, and the water was brown again, so I decided to flush with the hose one more time (which I didn't want to do) until I had clean water again. Drained from lower hose once more.

I also pulled the overflow and cleaned it, it had like an inch of mud/rust in it.

Installed a new Stant Premium 195* tstat and gasket.

Filled radiator with 1 gallon of straight Prestone, and then topped it off with 50/50 mix in radiator and overflow.

Let it run for 30 minutes, then drove around for an hour. It was great, held right at 210*, I was so happy, I was like, "I did it!". Then I decided to turn on the a/c to check it out. With the a/c on it rose a couple degrees while driving, but was fine. When I parked and sat for 15 minutes, it shot up and said I was overheating. This is driving me nuts.

I would like to thank everyone on all the forums from the stuff I have read, been an extreme help to me so far. XJ owners rock!

Any have any ideas?

The Auxiliary fan should come on when the temps come up, and when the A/C is turned on (regardless of temp - i think)
..... can u verify that the auxiliary fan is working and coming on when it;s supposed to?
Sounds to me like its not working the way it should.

First I would like to suggest you pull the radiator and turn it on its side and let the garden hose run and get it flushed out good. There is probably a lot of crud in the bottom of the side tanks. Second, check that fan clutch. When cold, rotate the fan. If it is stiff, the clutch needs replacing. Is there a shroud on the mechanical fan. If not, get one

Don't forget to check the belt driven clutch fan. Of course that wouldn't be the source of your corrosion. I would agree with pulling the radiator and flushing that our real well. But I would do a real good job flushing out the block. I've seen blocks that were really clogged up with rusty deposits, for whatever reason. I could be the source of the water that was used to dilute the anti-freeze, or just very old coolant. Either way, until you get nice clean water running through the system, I wouldn't expect improvement in the cooling ability.
Your experience doesn't say very much about the abilities of your mechanic.

I had "heat creep" on my 98 XJ for years. I'd have to drive 12 miles at 60+ mph and the temp would start creeping up. Finally fixed it. Three key areas.

Radiator, factory Mopar.
Replaced heater core (thanks Matt!)
Air flow. With aftermarket winch bumper needed more of an air dam to force air through the radiator.

I can drive 80 mph in 96 degree air temps. If I dog it a lot temp will rise but it holds and will cool over time.

Oh, and this will curl your hair. The old 4.0 and the new 4.0 had the same heating issue. At they are two completely different motors.

I swapped out the fan clutch and coolant temp sensor last night.

I did some driving today, without the ac and she did perfect on highway and in traffic on surface streets. After a while I drove for a while with the ac on full blast on the highway, and in traffic on surface streets, still did great.

I am hoping we got it licked and she'll be good for a while longer!

Good to hear !