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?

Replace the mechanical fan clutch and the radiator cap. Use a 16lbs cap. With a severely neglected cooling system you may have to use a chemical flush again.

Engine will get hotter after you shut it off...since water isn't circulating any longer. So, getting hot sitting for 15 minutes is normal. Should come back down if you re-start and let it run for a few minutes.

I wouldn't expect it to shoot up from say 210-215 to 260 after you shut off the car. The temperature will increase a bit, but not a few ticks on the dash gauge. Is the mechanical fan and e-fan running at full till when you turn it back on? You might put an IR thermometer on the thermostat housing to sanity check the gauge/sending unit. A new radiator cap costs about $5 and a fan clutch $35 at NAPA.

The fan clutches wear out over time. Sometimes they fail "on" (constant roaring), sometimes they fail "off" (can spin round and round with one swipe of the hand) and other times they just they're just old and tired and don't blow enough air.

I'd start with the radiator cap since its the cheapest and easiest, because a system at the proper pressure will have a higher boiling point (before it turns to steam). If your A/C feels on the week side around town but does OK on the highway, I'd plan to change the mechanical fan sooner rather than later.

OP: clarify when you parked and sat for 15 minutes, did you leave the engine running or shut it off?

Is it actually getting overheated, or are you just relying on the dash temp gauge? If the latter, be sure your gauge is accurate and good.

I had it running with the ac on when it got hot.

I picked up a fan clutch (I put the one in it now about 2-3 years ago) I picked up a temp sensor too. Advanced had a 20% off coupon on their mobile site. Which was nice

Drove home from work and she was just under 210° the whole way, I didn't have the ac on.

I'll put the parts on and see what happens. Figure there really isn't too much left to change...

So it's OK when driving, but heats up at idle? Does temp drop if you increase RPM while in park?

If your putting in the fan clutch, make sure your fan shroud is in good shape and complete. Also check your lower hose at idle, see if is collapsing.

I'll check the shroud I'm pretty sure it's in good shape. Last time it heated I popped the hood to check the lower hose for collapse, but it was in good form.

It is actually getting hot, right? Not just relying on the in dash gauge.

Yeah, mechanics said with the thermometer it only showed hot right in front of the water pump.

Got the fan clutch on, and coolant temp sensor. My son was excited I let him do the sensor. (He's 7) I'll get out an drive tomorrow and see what goes.

Well drove around for a while today getting estimates for a muffler repair and the temperature was fine. Drove around some more with ac on full blast. Stop and go traffic and highway the temperature stayed steady around 215/220. Didn't get close overheating. Appears that it was the fan clutch. Surprised the mechanics didn't suspect that.

Anyway with the time (and money) I've put into this ole XJ I've learned a lot and feel we have bonded more than ever.

So with new shocks, brakes, cooling system, catalytic converter, and muffler I hope we can roll around for a while yet to come.

Thanks everyone!

Glad it appears to be resolved with a good result.

You got the right attitude to be an XJ owner. Oh, and don't worry, it'll give you plenty more opportunity to "appreciate" it.

Hope you figured out that you are better off doing it yourself. You can even afford to make mistakes, compared to paying mechanics. Just stay tuned to the forum!

winterbeater said:

Hope you figured out that you are better off doing it yourself. You can even afford to make mistakes, compared to paying mechanics.

Click to expand...

There are some jobs you'll want to pay a pro for... and many, many more you can DIY if you're willing to put the time in. This, coming form a former auto mechanic. It always amazed me what people would pay us $750 to do, that they could have done themselves in the driveway.

Mostly brake work I will not do. Every car I've owned I've had to do water pumps and stuff so that isn't an issue. I've never flushed a system before until the other day, so I'm glad I was able to gain something from the experience.

I'm definitely going to try to be more preventative in the maintenance on this thing from now on.

Don't trust the mechanic on temp. These run hotter than normal cars anyway, so their "hot number" might be normal. ...change the temp send unit with a MOPAR brand. NO NO NO autozone senders.. trust me... did the same thing you did.... threw parts at a "mystery" overheat.... TWO BTW sending units were faulty....uhg.... just my 2 cents....