• NAXJA is having its 18th annual March Membership Drive!!!
    Everyone who joins or renews during March will be entered into a drawing!
    More Information - Join/Renew
  • Welcome to the new NAXJA Forum! If your password does not work, please use "Forgot your password?" link on the log-in page. Please feel free to reach out to [email protected] if we can provide any assistance.

99 XJ Sudden temp rise and sudden drop shortly after

jjnavarro

NAXJA Forum User
NAXJA Member
Hi All,
I'm hoping for help on a problem with my 99XJ that's got me and my mechanic stumped.
I recently had my auto transmission flushed and filled -routine maintenance. I took a camping trip last weekend and had the car packed with gear and people in hot (~90s) weather.
Going up hill on the freeway, my check gauges light went on and my temp gauge jumped from normal to one notch below max in a flash. I pulled over and checked my fans and coolant level. All fans were on (including aux) and coolant was ok.
After a couple of minutes, the temperature dropped as quickly as it rose in the beginning and all was good.

Later on I was going slower up a steeper hill. The same things happened except this time my oil pressure dropped to about 15 and I was leaking ATF. I checked my trans fluid level and it was well above max. Just like the first time, after a few minutes temp dropped to normal and all was good.

Any idea on what's going on?
 
Fully loaded climbing hills you need to shift the trans into 3rd gear and avoid Overdrive. Sounds like you're overheating the transmission. Since your trans lines hook up to your radiator, that would explain the sudden rise in temperature. You're describing a classic transmission overheat. ;) A person who is not right on top of the gauges like you would have the trans overheating and spurting out so much fluid it hits the cat and makes a white smokescreen. I forgot to downshift once while climbing a hill while loaded and it quickly rose and spit ATF all over the cat. :wave:
 
You might ask the shop what transmission fluid they used. ATF4+ is frequently, incorrectly used in the Jeep AW4 (even by the dealer) and has also been reported to cause excessive slipping and hence heating. The AW4 is not a Chrysler made tranny and does not take the Chrysler specific AT4+. It needs Dexron III.
 
jjnavarro said:
Going up hill on the freeway, my check gauges light went on and my temp gauge jumped from normal to one notch below max in a flash.
The exact same thing happend to me once. 1999 XJ, hot day, pulling a hill, Temp gauge jumped, I pulled over as quick as I could. Started her up agaiin and it has never happened again. I dunno......
 
First red flag is when you mention that the tranny fluid level is well above the max line. This is really not a good thing. Overfilling the transmission results in frothing and incomplete lubrication. Fluid level should NEVER exceed the max line on the dipstick (hot engine, fully run through gears, idling in park or neutral). More is not better here. Between ADD and MAX on the stick is better for your tranny than above MAX.

As far as your coolant overheat, yea....could be the use of overdrive. Avoid that on hilly terrain when towing or loaded to the gills with the Griswolds and the kitchen sink. When was the last time you had routine cooling system service (drain/flush/fill and replace thermostat if necessary). Always good time to review maintenance basics when there are symptoms.
 
Sorry for the old thread, but I had a similar problem this weekend in my '99. Ecksjay, you mentioned a sudden rise in temp indicating a tranny overheating. Just how sudden? Would it also fall back to normal temp just as suddenly?

(Relevant stats: '99 Cherokee Classic, 4.0, Auto, original radiator, flushed cooling system and installed new OEM thermostat about 4 months ago.)

Here's my story... Went camping/wheeling in the Shaver Lake area this weekend. I was pulling Tollhouse Grade at a good clip as I've never had an overheating problem. The Jeep feels a bit sluggish but I assume it's due to the almost 100 degree outside air temp. Suddenly, the "check gauges" light comes on and the temp gauge swings to the second to last mark. When I say suddenly, I mean in less than a second the needle went from ~210 to ~250. I slowed down and turned the heater on. About 30 seconds later, the temperature suddenly dropped from ~250 to ~210, again in less than a second.

I figured maybe it was a sensor error so I picked up speed again. A few minutes later, same thing occured again. A sudden increase to ~250 followed by a sudden decrease to ~210. All together, this cycle occured three or four times on my way up the grade. The rest of my weekend wheeling went off without any indication of my overheating issue.

So what could be the reason for such sudden changes in temp? It was almost like a thermostat opening and closing but the temperatures seem like they were too high for that. I was thinking turning on the heater could have been cooling the engine, but it seems that would cause a gradual drop in temp rather than a sudden drop. Sensor error? Air in the system? Blockage in the system being bypassed when the heater was turned on?

Any thoughts would be appreciated. I want to figure out just how big (or small) of a problem I have.
 
Just a thought..Is the temp gauge an actual gauge or more of a glorified idiot light like Ford has?
 
I don't think so. It rises slowly to normal operating temp as your engine warms up and you can see minor fluctuations in engine temp as you drive.
 
........ Suddenly, the "check gauges" light comes on and the temp gauge swings to the second to last mark. When I say suddenly, I mean in less than a second the needle went from ~210 to ~250. About 30 seconds later, the temperature suddenly dropped from ~250 to ~210, again in less than a second.

...So what could be the reason for such sudden changes in temp? ..

The radiator cap.

The radiator cap keeps the cooling system operating at 16 lbs of pressure. The pressure in the system keeps the coolant from turning to steam. (Remember your Physics lessons ?) If the radiator cap is weak, the coolant can instantly flash to steam and the steam will stall the flow of coolant through the water pump. What you see on the dashboard temperature gauge is the steam pocket forming and then returning to condensed liquid.
 
Make sure your torque convertor is locking up. If not, the tranny will generate a lot more heat.

2x on the radiator cap. They should be replaced at least every two years. It isn't a bad idea to replace the thermostat as well.
 
The radiator cap.

The radiator cap keeps the cooling system operating at 16 lbs of pressure. The pressure in the system keeps the coolant from turning to steam. (Remember your Physics lessons ?) If the radiator cap is weak, the coolant can instantly flash to steam and the steam will stall the flow of coolant through the water pump. What you see on the dashboard temperature gauge is the steam pocket forming and then returning to condensed liquid.

Having the exact same issue here too. Please correct me if I'm wrong, but if the radiator cap was not working correctly to keep the system at 16lbs, wouldn't we see something venting out the top? When this happened to me, I popped the hood immediately after pulling over and saw no signs of any over boil or steam escaping. No drips on the ground either. I'm going to put in a new sender since they are cheap enough. I take it this isn't normal activity for the temp gauge?
 
... If the radiator cap is weak, the coolant can instantly flash to steam and the steam will stall the flow of coolant through the water pump.

By the time you pull over and open the hood, any escaped steam is long gone.

How much does a new radiator cap cost ? Just buy a new one.

210* is the normal operating temp, anything over 220* is abnormal, sudden temperature spikes to the red zone are abnormal.
 
Last edited:
The radiator cap.

The radiator cap keeps the cooling system operating at 16 lbs of pressure. The pressure in the system keeps the coolant from turning to steam. (Remember your Physics lessons ?) If the radiator cap is weak, the coolant can instantly flash to steam and the steam will stall the flow of coolant through the water pump. What you see on the dashboard temperature gauge is the steam pocket forming and then returning to condensed liquid.

That makes sense to me. Seems like a logical explanation. I would think you'd see some sign of steam/coolant residue around your radiator cap when this happens, but maybe it all gets blown away by the airflow coming through your engine compartment before it has a chance to settle. I'll try the new radiator cap and see if that helps. It may be awhile before I get to test it out because there's just not that many big hills close to where I live.

Make sure your torque convertor is locking up. If not, the tranny will generate a lot more heat.

2x on the radiator cap. They should be replaced at least every two years. It isn't a bad idea to replace the thermostat as well.

How do you make sure your torque convertor is locking up? Just listen closely? This will be the first time my radiator cap has been replaced since my XJ was new in '99. I did change the thermostat about 4 months ago.
 
Well, almost a year later I finally pushed it again. I replaced my radiator cap shortly after my last post, but I once again experienced the exact same symptoms as I described in my earlier post. This time I was towing a 4x8 enclosed U-Haul trailer loaded with camping gear up Beasore Road out of Bass Lake. Same rapid rise to 250 degrees, same rapid drop to 210 degrees. Went through this about 5 or 6 times while climbing the grade. Slowing down and allowing my RPM's to drop from ~3500 to about ~2500 would cause the temperature to drop back to normal after about 20 seconds. I'm convinced it is a steam pocket forming somewhere in the system, I just want to know why it's happening and what I can do to prevent it from happening.
 
If you are developing a "steam"--air pocket in the coolant system that means your "open" cooling system is open.

Essentially somehow air is entering the cooling system. This shouldn't be happening. The radiator should be completely full, so should the overflow hose, and there should always be coolant in the recovery bottle and that coolant must always cover the end of the overflow hose in the bottle.

Coolant expands as it heats, the valve in the radiator cap allows expanded coolant out, through the hose, into the recovery bottle. When the system cools, the coolant retracts and that creates a vacuum and coolant is drawn back from the recovery bottle to fill it.

Ok, so how can air be entering the system? You could have a small leak somewhere. Not all leaks leave a puddle under the front end. Small leak at the WP weep hole can be nearly invisible--the fan blows away the coolant and the heat of the engine evaporates it too.

So, start with a visual inspection of the WP, t/stat housing, hoses, tighten all the clamps, look around the CTS sensor, look at the "freeze plugs", don't forget to try and check the ones at the back of the engine with an inspection mirror.

You can try a pressure tester, rent one at a chain parts store.

Now, as discussed earlier in the thread, the transmission puts an extra load on the cooling system, and when the trans is working hard, and the engine is working hard, and the ambient temperature is up, well--there you go.

Things I would do after checking for leaks:

1. Change your coolant mix from 50/50 to 30/70, 30 ethylene glycol and 70 distilled water. Ethylene glycol is a very good anti-freeze, however it isn't very good as a cooling medium. Run 30/70 late Spring to early Fall, then back to 50/50 for the cold season.

2. While you have the coolant out, run a radiator cleaner through it--you put it in and leave it for 3-6 hours of driving--can be over a number of days. 15 minute flushes just don't cut it for heavy deposits.

3. Consider replacing your OEM thermostat with a Stant SuperStat Premium 195 degree. The Stant SuperStat Premium has a built in V-passage that stabilizes engine temperature.

4. As you seem to tow and drive in the hills, consider adding a ZJ HD fan clutch. Some people think they don't operate at highway speeds--they are misinformed. They are thermal fan clutches controlled by a bi-metal spring on the front of the clutch. When ever the temperature of the air flow passing through the radiator and hitting the fan clutch is at 170 degrees (about 200 degrees for the engine coolant) the bi-metal spring starts to open the reservoir and the clutch will start to engage.

NAPA ZJ HD fan clutch, number 272310, $44. If you decide to get it, don't let the counter monkey sell you a MAX COOL fan clutch, it won't fit.

Good luck.

Post up with what you find.
 
I'm actually about to overhaul the entire cooling system in the next couple of days so I may never be able to track down the culprit if in fact air is leaking into the system somehow. I'm installing a CSF 3-Row, GMB Water Pump, Mopar Thermostat, NAPA XJ Fan Clutch (272318), new radiator and heater hoses, new hose clamps, and was planning on a 50/50 mix with Red Line Water Wetter added to it.

I was on the fence in regards to the fan clutch but decided on the XJ clutch due to the reports of the ZJ clutch making for a noisy fan. While I haven't tried the Stant thermostat, I like the check valve/air bleeder on the OEM variety. Admittedly, it does get hot here in the CA Central Valley, however 99% of my driving is FLAT. Depressingly so after having been accustomed to living in the hills. Aside from what seems to be a once a year overloaded camping trip up the hill on a 100+ degree day, my cooling system has always performed flawlessly.

In ten years and 90K miles, I've only changed the coolant once at 45K, the thermostat once at 45K, and the radiator cap once last year. Not exactly the best maintenance record. I know my radiator is starting to get plugged (nothing comes out the petcock when you open it) and I blew a radiator hose last week (thus the cooling system overhaul). I had noticed some crusty build-up (evidence of a minor leak) where my upper radiator hose connects to the radiator. I also noticed a small amount of leakage (once) coming from what appeared to be the crimp between the radiator and tank. Maybe one of these two problem spots is where air is getting into my system. If so, the new radiator and hoses ought to solve my problems. After replacing everything, I'll try to punish my cooling system again later this week on my way up to the Swamp Lake run. This is the grade where I had the "overheating" issue the first time around. I'll report back with the results...
 
Just a side note for searchers and lurkers: (Newer Open System)

-----BURPING THE XJ-----(OPEN SYSTEM)
Observe that the top of the whole cooling system is the top of the radiator, next highest is the cylinder head, Which just happens to be the hottest temperature in the system. Now observe the COOLANT RECOVERY TANK (CRT) is LOWER in relation to the filler neck (radiator cap) and cylinder head.

When you fill the system 'full' at the radiator cap there are still air pockets in the head.,and stray air tends to go there, this air is exactly where coolant is needed the most - at the TOP of the cylinder.

The easy way to get the air out of the system is to:
1. Fill the system with coolant. CRT to 'FULL" mark on the tank
2. PUT THE RADIATOR CAP ON AND LEAVE IT CLOSED!
3. Run engine to normal running temp with cabin heater on full heat.. (about 200*F give or take) About 5-10 minutes.
4. Note level in CRT hot.
5. Allow to cool several HOURS.
6. Note coolant level in CRT as it cools.
If level goes below 'ADD" mark then add coolant mix to CRT to keep between 'Full' and 'Add' . Do NOT allow level to go lower and pull air back into system. DO NOT OPEN RADIATOR CAP-ADD COOLANT TO CRT ONLY.
7. Repeat 3 - 6 a few times till levels hot and cold return to same places and no coolant needs to be added.

******IF RADIATOR CAP IS OPENED-GO TO STEP 2 AND START OVER.*****

This can be done over a few days as per your schedule, only takes a moment to pop the hood and eyeball the CRT level.

(routinely eyeball CRT level at gas stops and cold in the A.M. before startup say weeklyor so is a good habit!)

---IF CRT level is NOT changing- FIX the air leak - radiator to CRT---

Normal level change hot-cold is about 1/2 or 3/4 inch.

Starting with the left front of XJ elevated a few inches helps to work the air out to the CRT.

(CRT= air-out, coolant in. thats good!)

Good Luck,
Orange
 
Well, almost a year later I finally pushed it again. I replaced my radiator cap shortly after my last post, but I once again experienced the exact same symptoms as I described in my earlier post. This time I was towing a 4x8 enclosed U-Haul trailer loaded with camping gear up Beasore Road out of Bass Lake. Same rapid rise to 250 degrees, same rapid drop to 210 degrees. Went through this about 5 or 6 times while climbing the grade. Slowing down and allowing my RPM's to drop from ~3500 to about ~2500 would cause the temperature to drop back to normal after about 20 seconds. I'm convinced it is a steam pocket forming somewhere in the system, I just want to know why it's happening and what I can do to prevent it from happening.

Just to confirm, this isn't due to the torque converter unlocking and generating lots of extra heat from the tranny right?
 
Wow. I had no idea this was such a common problem. I ran into the same problem with my 98 XJ this weekend. (4.0, auto, 99 intake manifold, aftermarket air and exhuast headers back, 31" tires, 4.10 gears). I changed the radiator 18 months ago. (cheapo, not wise, but it was a warranty replacement). Changed the water pump and thermostat 8 months ago, Napa parts, 190 degree stat. Didn't know where to start, so I changed the thermostat to a 180 degree. First time it was an issue was yesterday, driving in hilly Montana country, and it did the spike and fall a couple times. Changed the stat, and it did it again. I thought it was A/C related, so I quit running the A/C. Today, the temp gauge wouldn't stop climbing. I was driving 65 on the highway and the temp was still reading at least 1 hash mark past 210. I'm subscribing to this thread because I need to fix this or I'm selling it and buying a new Toyota. :)
 
Back
Top