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  #1  
Old August 26th, 2008, 18:33
jjnavarro jjnavarro is offline
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99 XJ Sudden temp rise and sudden drop shortly after

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?
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  #2  
Old August 26th, 2008, 20:01
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ECKSJAY ECKSJAY is offline
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Re: 99 XJ Sudden temp rise and sudden drop shortly after

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.
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  #3  
Old August 26th, 2008, 21:54
lawsoncl lawsoncl is offline
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Re: 99 XJ Sudden temp rise and sudden drop shortly after

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.
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  #4  
Old August 26th, 2008, 22:04
Blazair Blazair is offline
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Re: 99 XJ Sudden temp rise and sudden drop shortly after

Quote:
Originally Posted by jjnavarro
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......
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  #5  
Old August 30th, 2008, 10:41
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birchlakeXJ birchlakeXJ is offline
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Re: 99 XJ Sudden temp rise and sudden drop shortly after

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.
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  #6  
Old August 4th, 2009, 20:47
fyrfytr1717 fyrfytr1717 is offline
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Re: 99 XJ Sudden temp rise and sudden drop shortly after

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.
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  #7  
Old August 4th, 2009, 21:30
Chrisc321 Chrisc321 is offline
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Re: 99 XJ Sudden temp rise and sudden drop shortly after

Just a thought..Is the temp gauge an actual gauge or more of a glorified idiot light like Ford has?
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  #8  
Old August 4th, 2009, 22:19
fyrfytr1717 fyrfytr1717 is offline
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Re: 99 XJ Sudden temp rise and sudden drop shortly after

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.
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  #9  
Old August 5th, 2009, 07:49
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Re: 99 XJ Sudden temp rise and sudden drop shortly after

Quote:
Originally Posted by fyrfytr1717 View Post
........ 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.
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  #10  
Old August 5th, 2009, 10:37
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Re: 99 XJ Sudden temp rise and sudden drop shortly after

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.
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  #11  
Old August 5th, 2009, 13:39
ragnard ragnard is offline
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Re: 99 XJ Sudden temp rise and sudden drop shortly after

Quote:
Originally Posted by Tim_MN View Post
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?
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  #12  
Old August 5th, 2009, 16:28
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Re: 99 XJ Sudden temp rise and sudden drop shortly after

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Originally Posted by Tim_MN View Post
... 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.
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Last edited by Tim_MN; August 5th, 2009 at 16:31.
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  #13  
Old August 5th, 2009, 17:01
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winterbeater winterbeater is offline
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Re: 99 XJ Sudden temp rise and sudden drop shortly after

XJ's aren't overheating until they boil. The aux fan on a 2000 doesn't even kick on until 223 F and kicks off when it cools down to 217.
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  #14  
Old August 5th, 2009, 19:57
fyrfytr1717 fyrfytr1717 is offline
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Re: 99 XJ Sudden temp rise and sudden drop shortly after

Quote:
Originally Posted by Tim_MN View Post
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.

Quote:
Originally Posted by old_man View Post
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.
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  #15  
Old July 30th, 2010, 22:37
fyrfytr1717 fyrfytr1717 is offline
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Re: 99 XJ Sudden temp rise and sudden drop shortly after

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.
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