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  #1  
Old March 30th, 2019, 21:12
Jwasser813 Jwasser813 is offline
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4.0L XJ Auxiliary cooling fan activating at high temperature - overheating?

1995 4.0 L XJ sport

According to dashboard Temperature gauge the auxiliary fan does not activate until the temperature reaches red line when at idle or stop and go driving. Cool just fine when driving at highway speed’s even as low as 40 miles an hour. I recal seeing it get up there periodically in the past but hadn’t noticed it being this regular.

Replaced the pump, thermostat, and the CTS. I also switched around the relays with a matching one until the new one I ordered arrives. Hoses on both sides of the housing are hot so coolant seems to be flowing. One suggestion I saw was to was considering getting a laser temp thermometer to test the temp at the thermostat housing since the dash gauge an be unreliable in XJs. Any suggestions greatly appreciated. Thanks.
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Old March 31st, 2019, 07:16
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Re: 4.0L XJ Auxiliary cooling fan activating at high temperature - overheating?

Why is the Jeep overheating at idle and/or stop n go traffic ? Is the cooling system routine maintenance current, and the mechanical fan clutch is fully functioning ?


Confirm the dashboard indications with an IR temp gun. Did you replace the CTS that runs the e-fan, or the CTS that runs the gauge ? Did you use good quality sensors that read true ?
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  #3  
Old March 31st, 2019, 19:14
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Re: 4.0L XJ Auxiliary cooling fan activating at high temperature - overheating?

Somethign is off. The 95 uses two different temp sensors. The one in the top back driver's side of the head is what provides data to the gauge, the one in the thermostat housing provides data to the PCM for E-fan activation and fueling data.

It should activate the E-fan at 217 degrees or so. So either your head mounted sensor is out of wack (or the wiring or gauge is) or the thermostat housing temp sensor is out. There is a test procedure using OHMs to measure OHMs vs Temperature.

If you disconnect your thermostat housing temp sensor it should also make the fan come on while the engine is running.

Do you have a FSM for your Jeep?
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Old April 1st, 2019, 09:08
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Re: 4.0L XJ Auxiliary cooling fan activating at high temperature - overheating?

remember it's the front sensor near thermostat that controls when the E fan to comes on.

Can the gauge sensor, near the rear of the engine be wrong? Would there be any reason for the rear of the engine near the firewall to be 20-40F higher than the front? blockages, etc. verify w/$10 infrared temp sensor from harbor freight
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  #5  
Old April 1st, 2019, 20:24
Jwasser813 Jwasser813 is offline
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Re: 4.0L XJ Auxiliary cooling fan activating at high temperature - overheating?

Thanks to everyone for responding.

I replace the the coolant temp sensor that controls the fan and fuel mixture with a Crown Automotive CTS. Showed the same as it did with the one I replaced. Based on everyone's advice, since so many parts were replaced, and the new sensor gave the same readings when the fan activated I figured t might be the temperature sending unit rather than the CTS on the thermostat housing.

I looked at the Infrared thermometers at Harbor, but the only ones at the one by me had terrible reviews. I ended up with a General brand one which had pretty good reviews for $22 from home depot. With it placed on the thermostat housing the fan went on at 221 degrees according to the IR. I tested the IR on some things in my freezer which is very accurate and the IR read consistently 3 degrees warmer than the freezer setting. Now I'm thinking its the Temperature Sending Unit. I'm going to check the connection and if reseating it doesn't fix the issue I'll try replacing the sending unit.

As I understand it the sending unit is fragile and in a difficult to access spot. Any suggestions on replacing it?

Thanks again for all the suggestions!
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Old April 1st, 2019, 20:26
Jwasser813 Jwasser813 is offline
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Re: 4.0L XJ Auxiliary cooling fan activating at high temperature - overheating?

Quote:
Originally Posted by devildog0 View Post
Somethign is off. The 95 uses two different temp sensors. The one in the top back driver's side of the head is what provides data to the gauge, the one in the thermostat housing provides data to the PCM for E-fan activation and fueling data.

It should activate the E-fan at 217 degrees or so. So either your head mounted sensor is out of wack (or the wiring or gauge is) or the thermostat housing temp sensor is out. There is a test procedure using OHMs to measure OHMs vs Temperature.

If you disconnect your thermostat housing temp sensor it should also make the fan come on while the engine is running.

Do you have a FSM for your Jeep?
No I don't have a FSM. Just Haynes.
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Old April 2nd, 2019, 05:21
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Re: 4.0L XJ Auxiliary cooling fan activating at high temperature - overheating?

Quote:
Originally Posted by Tim_MN View Post
Why is the Jeep overheating at idle and/or stop n go traffic ? Is the cooling system routine maintenance current, and the mechanical fan clutch is fully functioning ?


Confirm the dashboard indications with an IR temp gun. Did you replace the CTS that runs the e-fan, or the CTS that runs the gauge ? Did you use good quality sensors that read true ?
This^^. Fan clutch likely not up to task and electric fan can't keep up.
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  #8  
Old April 2nd, 2019, 06:55
Jwasser813 Jwasser813 is offline
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Re: 4.0L XJ Auxiliary cooling fan activating at high temperature - overheating?

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Originally Posted by cruiser54 View Post
This^^. Fan clutch likely not up to task and electric fan can't keep up.
I was thinking the same thing this morning!!! Just ordered one. The dash gauge is definitely off, but the mechanical clutch should be keeping it from creeping up.

I saw that someone else on another forum was having a similar issue and found their dash gauge was off by 20 degrees as well so I guess that is an issue sometimes.

I'll keep everyone posted.

Thanks
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Old April 2nd, 2019, 13:24
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Re: 4.0L XJ Auxiliary cooling fan activating at high temperature - overheating?

On my 96---- Snap-on scan gauge reading temp from the sensor in the T-stat housing will read 15* less than the Autometer gauge sender located at the rear of the head.

So 195*(what the ECU sees), 210*-what you see.

Your problem is with clutch fan ,I see you didn't,t replace radiator cap a 16# is what is called for.
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  #10  
Old April 9th, 2019, 17:41
Jwasser813 Jwasser813 is offline
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Re: 4.0L XJ Auxiliary cooling fan activating at high temperature - overheating?

UPDATE:

I replaced the fan clutch and the dash gauge now maxes out at 230 on the dash gauge in stop and and go traffic, although the outside temp was only 58. I checked the connection at the sending unit; the clip on the wiring harness is missing b t the rubber from inside is there and was/is just pushed in to the unit - perhaps why the discrepancy between the CTS and the dash gauge.

Can't find the clip for the sending unit on line so when I get a chance to I'll go toe U Pull It junk yard and try to find one. Other than that I guess I'll have to live with the the dash gauge reading higher than it should.
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  #11  
Old April 10th, 2019, 00:26
cinema cinema is offline
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Re: 4.0L XJ Auxiliary cooling fan activating at high temperature - overheating?

Your temps seems normal to me. Maybe a bit high if youre not stopped for excessively long times but if the e fan comes on at 221 (normal) and kicks the temp back to 210-215 you are within range. If it stays cool while driving and on the freeway you are ok. May have a clog or blockage somewhere if easily hitting 230 in stop and go on cool days.
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  #12  
Old April 10th, 2019, 00:29
cinema cinema is offline
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Re: 4.0L XJ Auxiliary cooling fan activating at high temperature - overheating?

Also i see u are in brooklyn. Means long times stuck in traffic im guessing. I think your temps are normal.
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  #13  
Old April 10th, 2019, 04:29
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Re: 4.0L XJ Auxiliary cooling fan activating at high temperature - overheating?

Even if temps are 100° outside, the coolant should stay at about 210 -220° in traffic if the cooling system is functioning properly. The mechanical fan and the e-fan together have enough air flow to keep the temp below 230°.


Quote:
Originally Posted by Jwasser813 View Post
I replaced the fan clutch and the dash gauge now maxes out at 230 on the dash gauge in stop and go traffic, although the outside temp was only 58.

If the gauge reading is reading true and confirmed by an IR temp gun, you are not done with your cooling system maintenance.
__________________
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.

Quote:
Originally Posted by bimmerjeeper

I'm starting to realize people on the Jeep forums are highly expert mechanics .....
Quote:
Originally Posted by soyjer

Tim MAY be 100% correct, but why would a person automatically pick him as the expert .....
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  #14  
Old April 11th, 2019, 21:33
Jwasser813 Jwasser813 is offline
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Re: 4.0L XJ Auxiliary cooling fan activating at high temperature - overheating?

Quote:
Originally Posted by cruiser54 View Post
This^^. Fan clutch likely not up to task and electric fan can't keep up.

The dash gauge is definitely off. I checked temperature at the thermostat housing and when the temp on the gauge is at red line (240) the IR gun reads 221 and e fan kicks on. I checked the IR gun against a known freezer temp and it read three degrees warmer (within margin of error for that gun) and that would put engine temp right at 218 when the fan kicks on (same as with the old and new CTS) and the dash gauge off by 22 degrees. Now that I installed the new fan clutch it never gets up to the that point even in serious stand still traffic (NYC rush hour traffic), so when the dash reads 230 in traffic its actually about 208. As I said above the clip for he temperature sending unit is broken and the rubber and wire form inside are just pushed in which is probably affecting the dash reading.

thanks everyone.
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