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Overcooling?

S

stardust2280

NAXJA Forum User
Location
Wyoming
2001 Jeep XJ, 3.5" lift w/ 31" tires, aftermarket aluminium radiator.

I have having problems with my Jeep not getting up to temperature. If I let it idle for awhile (30+ mins) it almost gets to 210, but then drops back down to between the second and third tick marks when I start to drive it, which obviously is running much to cool. The heater is suffering due to the engine not heating up, so my heat is mildly hot at best (but it is better at idle when the engine is almost to 210). I bought this XJ with a cracked head, and replaced it with a new TUPY head.

I have:

Replaced T-stat with a 205, which improved the running temperature only marginally
Replaced water pump, t stat housing, and radiator hoses
Triple checked coolant levels
Replaced head
Replaced fan clutch with a new one
 
Move down south to Texas? :eek:
 
Old_man had one doing that and refusing to go closed loop, and thus wasting gas as well. He fixed it with a new CTS sensor. Old was stuck telling the ECU the engine was ice cold, and the ECU refused to try and go closed loop. Rich burn it seems does not produce enough heat up north in the winter?
 
Ecomike said:
Move down south to Texas? :eek:
Click to expand...

Good call. Shout us up when you get there,...we could enjoy a cold one or two.

stardust2280 said:
2001 Jeep XJ, 3.5" lift w/ 31" tires, aftermarket aluminium radiator.

I have having problems with my Jeep not getting up to temperature. If I let it idle for awhile (30+ mins) it almost gets to 210, but then drops back down to between the second and third tick marks when I start to drive it, which obviously is running much to cool. The heater is suffering due to the engine not heating up, so my heat is mildly hot at best (but it is better at idle when the engine is almost to 210). I bought this XJ with a cracked head, and replaced it with a new TUPY head.

I have:

Replaced T-stat with a 205, which improved the running temperature only marginally
Replaced water pump, t stat housing, and radiator hoses
Triple checked coolant levels
Replaced head
Replaced fan clutch with a new one
Click to expand...

I worked in Des Moines IA in 2007 up until a few days before Christmas. My XJ did not have a mechanical cooling fan then (and still do not) just 2 electrical fans that came on between 110 and 115 degrees on the dash. At highway speeds when the temps were 40 degrees or lower, my engine temperature stayed about 165 degrees, that is with the heater on. The heater temperature also stayed low.

For a Caribbean boy who lived most of his life between 75 and 85 degrees I promptly covered half the radiator with card board. And my XJ had and still have all items related to cooling being OEM products purchased at the Jeep/Chrysler dealer. Ecomike mentioned the possibility of a bad CTS. Check that all the mechanicals and electricals are working properly.

Oh! Over the almost 18 years I have owned XJ's there are not many thermostats out there that performs like those you get from the dealer.
 
Yup test your coolant temp sensor. Ignore the part of this video where they talk about the coolant temp SENDER on the back of the head the newer XJs use the thermostat housing sensor to both provide info to the computer and the dash gauge.

 
I'd suggest getting one of the bluetooth OBDII dongles, then the Torque app for your phone (or plug in a real OBD scanner) and see what the computer thinks the temperature is. Or, just go straight for the CTS. Also maybe blow out the heater core if the heater function is your main problem. FWIW I saw a stock XJ obviously daily driven a lot in the mountains with a piece of cardboard in front of the grill. I live in Montana and don't need to resort to that for excellent heater function in my 1996 or 2000's but YMMV.
 
Cardboard works in Minnesota, and CTS testing is required. Don't forget to flush the heater core.
 
I believe the CTS on this year XJ supplies info to the temperature gauge and computer. When a set temperature is reached, the computer activates the fan relay to turn on the electric cooling fan to cooldown the coolant. CTS are typically thermistors, with the Negative Temperature Coefficient (NTC) thermistor being the most accurate. Available literature indicates ALL thermistors, operating in the temperature range of XJs, start to drift in electrical resistance after about a year. If the thermistor always indicates a cool engine, the computer never activates the fan relay to turn on the electric cooling fan and overheating results. Likewise, as previously mentioned by others, if a thermistor is always telling a computer the engine is cool, the computer will supply more fuel to the engine. It appears that CTS (i.e. thermistors) should be replaced on a yearly basis since they all drift in electrical resistance after about a year. Likewise, most CTS are only warrantied for 12 months.

Best regards,

CJR
 
Yearly CTS replacement is a bit extreme, as the CTS is easy to test to determine if it is still providing accurate data. Smart Phone apps can also be used monitor CTS data. Cheap Chinese clone CTS are very prone to inaccuracy due to inferior materials and manufacturing processes.
 
Tim MN,

Where do I find the resistance or voltage values, for different temperatures, to test a CTS? I looked in my 2000XJ FSM and couldn't find any. I would suspect the CTS would need to be tested at room or ice temperatures and at high temperature, like boiling water, to see if the resistance is drifting/changing at either value. Likewise, I would suspect the computer is looking for specific voltages in order to on-off cycle the fan relay at the specified coolant temperatures cited in the FSM.

Best regards,

CJR
 
OP

I've got the same problem. Tried every thermostat I could find.

Infrared meter confirms its running cold. Currently running 205 tstat. On warm up, engine reaches 205, then tstat opens, and runs about 170.

I have seen one guy who put a diaphragm in his coolant line to limit flow and it helped bring his temp back up.

Here are my theories:

1) New t-stats may have weaker springs and are not strong enough to close the system after opened, while engine is running
2) New water pumps are pushing too much coolant and overpower tstat. Once it's opened, there is too much force produced by the water pump for tstat to close.

Whose pump do you have?

Anybody have any thoughts on these theories?
 
Just reread your post. First off what brand T-stat did you use? I would replace it first, with a Mopar, or at worst a Murray brand made in Israel. The one you have may be allowing too much coolant flow. May even be stuck open????

Also test the O2 sensor and see if it's working properly, and check the exhaust manifold for any cracks that may be biasing the O2 sensor data and making the ECU run the engine too rich. Cracks can make the exhaust look lean when it is not, forcing the ECU to run it even richer, thus takes forever to heat up.

Barring those two or a CTS issue, the lift and any aftermarket cooling mods (radiator?) that make it cool better, may be adding to your grief. Cardboard cover may be the cheap fix. Also make sure the E-fan is not stuck on running 24/7????? From a stuck relay or???

stardust2280 said:
2001 Jeep XJ, 3.5" lift w/ 31" tires, aftermarket aluminium radiator.

I have having problems with my Jeep not getting up to temperature. If I let it idle for awhile (30+ mins) it almost gets to 210, but then drops back down to between the second and third tick marks when I start to drive it, which obviously is running much to cool. The heater is suffering due to the engine not heating up, so my heat is mildly hot at best (but it is better at idle when the engine is almost to 210). I bought this XJ with a cracked head, and replaced it with a new TUPY head.

I have:

Replaced T-stat with a 205, which improved the running temperature only marginally
Replaced water pump, t stat housing, and radiator hoses
Triple checked coolant levels
Replaced head
Replaced fan clutch with a new one
Click to expand...
 
1993 and 1988 listed here:

https://www.cherokeeforum.com/f2/coolant-temperature-sensor-testing-188821/

Not sure of 1996 OBDII changed the HO data?

CJR said:
Tim MN,

Where do I find the resistance or voltage values, for different temperatures, to test a CTS? I looked in my 2000XJ FSM and couldn't find any. I would suspect the CTS would need to be tested at room or ice temperatures and at high temperature, like boiling water, to see if the resistance is drifting/changing at either value. Likewise, I would suspect the computer is looking for specific voltages in order to on-off cycle the fan relay at the specified coolant temperatures cited in the FSM.

Best regards,

CJR
Click to expand...
 
Ecomike,

Thanks for that info on the CTS resistance vs. temperature data. Since high temperature eventually causes drift in resistance, I would suspect the best test would be to monitor the drift of resistance in boiling water (212F) to see if the resistance drifts outside the range of resistance spec'd in the table.

Best regards,

CJR
 
Where is this drift of CTS resistance on the sensor story coming from?

I am aware of oil and dirt fouling being an issue for the response time of the ITAT air temp sensor, but first I heard of the CTS not lasting decades. Bad new ones out of the box I hear are common.
 
Ecomike,

Here you go! Do a search for "QTI White Paper, Negative Temperature Coefficient Thermistor by Gregg Lavenuta-QTI Engineering Department."

Likewise do a search for "Navsea, Thermistors"

Both sources cover thermistor drift and the temperatures and time duration where drift starts. Likewise the sources cite NIST, Mil Handbook, et.al.

If you have trouble finding the documents let me know and I'll try to attach my copies and send them to you.

Best regards,

CJR
 
Thanks, but looking at this one,


https://www.thermistor.com/sites/default/files/white-papers/T150-Series-Stability.pdf

I am not sure I would be too concerned
about a .08 *C drift in 12000 hours on my CTS in a 30 year old 292,000 jeep. :laugh3:

Hell the loose corroded sensor connections have 10 times that error in 30 years? Like maybe 0.8 C

I'll let the O2 sensor correct for that and worry about 50% errors in the TPS sensor and grounds.


CJR said:
Ecomike,

Here you go! Do a search for "QTI White Paper, Negative Temperature Coefficient Thermistor by Gregg Lavenuta-QTI Engineering Department."

Likewise do a search for "Navsea, Thermistors"

Both sources cover thermistor drift and the temperatures and time duration where drift starts. Likewise the sources cite NIST, Mil Handbook, et.al.

If you have trouble finding the documents let me know and I'll try to attach my copies and send them to you.

Best regards,

CJR
Click to expand...
 
Ecomike,

Every time I response, the Reply to Thread times out. You need to search for the sources I suggested. My QTI indicates "excessive" drifts at the temperature range of our XJ CTS. Likewise, the Navsea cites drift failures. Since there are many types and mfgers of thermistors, our CTS need to tested. Best way is to buy a new CTS, measure it at 212F, run it in an engine for a year, pull it and measure the resistance again at 212F to see what the resistance drift is.

Best regards,

CJR
 
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