except the sensor at the rear was removed in later years. Temp is controlled from the one on the housing

 

On the newer models they eliminated the temp sensor in the rear. The sensor located at the thermostat housing feeds both the PCM for engine management decisions and the gauge on the console.

 

do you know what year that the rear sensor was removed? I know 97 up for sure but was it sooner?

 

dont think so, i think the revision's first year was 97. i just researched a forum post from another gent with a 96, he had two sensors.

 

Ok good info
my 96 has both front and rear so your probably right about 97 up

 

running around the grocery store right now so not looking too hard through tbd thread, but just for clarification what year is the jeep in this thread haha

 

Not sure looks like 2000 or so in the pic

 

good to know smokey. thanks. logging that fact in my memory.

 

It's a 1997, sheesh!! Haha

----------------

Ok I finished the water pump install.

Just got got back from a test drive. It's been greatly improved! But it's not perfect. It didn't boil over but the temp started to creep up VERY slowest after about 25 minutes of 75mph driving. Last time, when it overheated, it was after only 5 minutes of 65mph driving! AND its way hotter today then it was then, temp was just about 90 today. AND I didn't have the Water Wetter in the coolant like I did before. Right now I have 25/75 antifreeze/water (distilled).

i drove around different highways for about an hour experimenting with different driving speeds and using the heater core to controls temps further. I found that it was fine at 65 but not at 75mph!

So, much better, but like I said the temp did start to slowly creep up and that's not good enough when I have to drive 9 hours through hot-as-hell western Kansas. My plan is to get it perfect, and then add the Water Wetter which will insure that it can handle going up a mountain at high elevations when the water boils over easier. Actually, I'm told that the Water Wetter just allows you to run with more water which cools better than antifreeze, it raises the boiling temp.

I think I'll try flushing it some more with some sort of acid or detergent.

and I'm also fairly sure I'm going to put some hood vents in.

after the hour long test drive, I took some under hood temp readings with a temp gun. Here they are:

• upper radiator hose: 219
• lowwr radiator hose: 169
• top of air box: 120
• air intake near #2 cylinder: 188
• air I take near #5: 215
• Inner fender: 142
• firewall: 127

what do you guys think?

-------------------------------------------------

EDIT

I'm editing this 8 months later for anyone who found this thread while looking for help with their own XJ overheating issues, so you can know what happened.

At the moment, the problem is not fixed. I improved it enough to drive to Colorado and back in the middle of June, but it was a nice 80 degrees and I still had to pull over to the side of the road so it wouldn't over heat (once time though I didn't do that fast enough and it boiled over).

My plan is to replace the radiator again just in case it's not a good one or it's full of rust that was dislodged from the engine, and convert to electric cooling fans. And I might as well test for a blown head gasket a third time before doing that.

Here's a round up of everything else I did:


I ripped out the AC condenser from in front of the radiator.
The reason I removed the AC condenser was to free up air flow to the radiator and because the AC was toast anyways. All the gas leaked out.

Now I'm the biggest tree hugger ever and the environment was one of my top concerns when thinking about removing the compressor. I decided to quickly check the pressure in the AC system by quickly letting out a tiny bit through the valve and listening to it. When I did that the tiniest little puff came out and that was it. What would have been even more irresponsible is if I tried to recharge it with new gas and all that would have just leaked out in less than a year (I saw on one of the old service receipts that they recently charged the AC less than a year ago). Thankfully the ozone layer is recovering nicely (not at all related to climate change BTW).

And I attached the transmission oil cooler to the radiator now that the condenser is gone, and positioned to be in front of the belt-driven fan instead of the electric fan which is usually not spinning

Some info I've gathered on flushing out rusted, scaley cooling systems

Aside from the weak stuff from the auto parts stores, these are the chemicals people report using:

• oxalic acid - really good at removing rust. Can be purchased as "wood bleach" for about $10 a little tub from a good hardware store
• Sulphamic acid - really good at removing lime and hard water scale and old antifreeze crud. Can be found as "tile and grout cleaner"
• citric acid - this is what Mercadez Benz dealerships use supposedly. Can be purchased from them, or from a good hardware store
• Motorcraft VC-9. This is reportedly very very good stuff, it's used by Ford dealerships to clean the iron blocks and heads of diesel motors which have a problem with rust clogging the oil coolers somehow... Can be purchased from Ford dealerships for around $30
• dishwasher detergent - another one that many people swear by
• CLR - most people agree this is too aggressive for aluminum radiators but many people swear by it

I bought a little tub of oxalic acid for around $10 bucks from my local hardware store. Will be putting it into the cooling system very soon, keep it in there for a few days of driving, drain it out and then pull the thermostat out to take a peak and see if it's any cleaner in there.

Hood vents are in the mail, should arrive after the weekend.

Colorado or bust!!

I used the Oxalic acid



I drained the radiator through the lower hose then reattached it. Mixed the oxalic acid crystals with hot water and poured it into the radiator through the filler neck. The crystals didn't dissolve in the warm water right away though and I had to kinda spoon it all in there.

After driving it around for two days, I drained it and this is what came out:



This time I completely flushed the system and removed the thermostat. The thermostat had a yellowish coating on it. At first I thought the metal was etched by the acid but I could scratch off the coating with a knife.

And this is what the inside of the head's coolant passages looked like after the acid flush:



For comparison, this is what it looked like before the acid flush but after flushing with both Blue Devil and Prestone:



So much better but not squeaky clean.

I'm not sure if I should be concerned about the yellow coating inside there or not, but when I filled the cooling system back up I put another bottle of Blue Devil flush additive in there with distilled water and now I'm driving it around and will flush that all out today or tomorrow.

I drove for about an hour on the interstate today and the needle never started creeping up at all! Stayed put right at around 200. (I have a 180 thermostat and will put a 195 in there soon).

So.. All fixed!!!

I flushed the cooling system for hopefully the last time today

Three days ago I filled the cooling system with pure tap water and one bottle of Blue Devil radiator flush. This is what came just now:



So as you can see there was plenty of rust/crud that the flush additive was able to get out after the oxalic acid. It also removed most of the yellow coating:



Not perfect but looking more and more like bare metal

The thermostat before and after the blue devil flush:




And here's the inside of the aluminum thermostat housing, I think the oxalic acid noticeably etched it:



After I put it all back together I hoped in my pickup to get some distilled water and antifreeze but the fuel hose was dry rotted and I spilled half my gas tank in the Oreilly's parking lot. A day working on my trucks is still better than a day in the office though!

 

My late 96 XJ had similar but not quite as bad overheating a year ago. XJ is original owner 101K miles all in Arizona with original HD cooling system. Before I rebuilt the entire system I flushed several times with prestone flush but overheating remained. I ordered an original three core HD radiator, pump, hoses, belt and 180 degree thermostat. I also got some oxalic acid ( wood bleach from Amazon) and many gallons of distilled water. I backflushed thru the heater hose, thermostat out, with the prestone kit and tap water until it ran clear then put in the oxalic acid and burned out the old parts for a couple of days driving. Then hose backflushed again and flushed with distilled water three times to get rid of all the tap water. Once I had everything clean I put in all the new parts and filled with 75% distilled water 25% antifreeze. Water cools and flows much better than antifreeze so summer and my climate a 75% distilled water to 25% antifreeze is best. After rebuild the system was better but still got warm in extreme conditions with my new rebuilt AC running so I replaced the HD ( not standard ) fan clutch. The HD clutch sounds like a mini tornado under the hood but moves much more air and solved the overheating problem. Yesterday I ran on the Phoenix freeway with 112 in the shade and AC blasting comfortably on high thru rush hour traffic. Road traffic temps typically 120 - 130 here.
Since this OP has replaced everything I would suggest putting in the old parts and hose flushing with thermostat out engine running until clear, then burning out with oxalic acid to clean out the junk, hose flush again then flush several times with distilled water to get all the tap water out. Put in new parts including an HD fan clutch ( got mine from NAPA ) and button up.

I have a few other issues namely momentary engine cutouts when warm but no overheating anymore.

 

I know this is an older post, but I had the same problem and wanted to help someone that may have the same issue. I replaced the entire cooling system, milled the head with new head gasket, replaced all my bad sensors. It would still heat creep at anything over 75mph or over 3000 rpm’s. It turned out to be the EGR valve, it was opening when I hit 3000 rpm’s which is what 75mph would do. It would open and lean out the fuel mixture and run it super lean and that would overheat it. I just unhooked the vacuum line to my EGR valve and it stopped overheating even at 80mph going uphill. Now, if your EGR valve is bad and it’s not the vacuum that is opening it up, then you will need a new EGR valve or block off plate. I have to pass emissions so I had to buy a new transducer and vacuum solenoid. I used a Ford transducer and vacuum solenoid. The solenoid requires a pigtail you have wire into the old wires. I used 1997 F250/150 parts.

 

Oh wow, I wonder if that was my problem too.

Like you, I replaced the entire cooling system and rebuilt the head. It was warped. All my efforts with flushing the cooling system shown in this thread weren't enough. Actually, I flushed it one last time with Evaporust's radiator flush product. And it was absolutely rust free after that, totally spotless. But was still overheating. I replaced the copper radiator with an aluminum one but didn't change anything. That's when I figured, even though I had no symptoms of a bad head gasket other than overheating, that maybe exhaust gasses was getting into the coolant only when driving at high speed/rpms. Off came the head and it was warped. Rebuilt it and it was much better.

After all of that I was able to drive 800 miles in the middle of July in the desert, which would have been impossible before. But while in Colorado and going up Monarch pass, a steep and long highway road, it overheated badly when the transmission dropped into second gear yet I still tried to keep the speed around 50 mph. After that, it overheated much easier and we had to drive back home at night when the outside temps were much lower.

Back home, I took the head off and it was not warped. New head gasket. Put it back together and it would still get too hot on the highway. Only the highway though. I did one last road trip in November before selling it and letting it be somebody else's problem.

I never checked the EGR valve! Goddam EGR emissions crap. One day I will have an all electric jeep and this won't be a problem!

 

Now I won’t replace the water pump or thermostat because I know and have confirmed both are functioning properly, and that my heater core is not clogged. My jeep also isn’t over heating at highway speeds but at anything more than an idle. Any tips for me?

 

What year? My first suspicion would be a bad fan clutch. If you can spin it when the engine is hot and the engine is off, it's probably bad.

 

brand new one of the first things replaced as the old one was completely spinning freely, and it couldn’t even idle without over heating