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  #1  
Old July 3rd, 2014, 15:09
Jaren1 Jaren1 is offline
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So bad temp sender?

I would like to start off by saying Hello and that this is my first time here and this is my first XJ. I did own a 2002 JGC a few years ago, loved it. Anyway, I just picked up my 98 Cherokee yesterday. I noticed that it seemed like it was running very cool. It was barely getting above the hash just above the 100. Even with the 90 degree temps we had yesterday. Drove it home today and turned the heater on, ambient temp outside was about 85 degrees. The heater got very very warm, I would say getting close to uncomfortable on my hand. Got home and left it running with the AC on. The top rad hose was uncomfortable to hold for more then a few seconds.

I took a little IR thermometer that I have and did readings on the Tstat housing and the top rad hose. To me they seem fine?

Here is the reading from Tstat housing


Here is the reading from the upper rad hose


And here is what the dash gauge looks like just after those readings


Gas mileage says its about 15.8 with mixed highway and city, just reset it this AM. So what do you all think. Thanks for the help. I did search a bit today and couldnt find a definitive answer, just some general clues.
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Old July 3rd, 2014, 15:21
md21722 md21722 is offline
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Re: So bad temp sender?

I don't have the FSM handy to see if it has ohm readings for the sensor. I'd think it could be the sending unit, dash gauge, or wiring. Most likely the sending unit. I hear dealer units work best (for any sensor) though NAPA Echlin is a good choice. Stay away from the others. Oil pressure seems a bit low also. May want to put a mechanical gauge on it. The oil pressure senders fail all the time. Sometimes they fail and the dash gauge is pegged at 80 and other times they just read low. Or your engine is worn. 20 or more is more appropriate for hot idle.
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Old July 3rd, 2014, 15:27
Jaren1 Jaren1 is offline
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Re: So bad temp sender?

Quote:
Originally Posted by md21722 View Post
I don't have the FSM handy to see if it has ohm readings for the sensor. I'd think it could be the sending unit, dash gauge, or wiring. Most likely the sending unit. I hear dealer units work best (for any sensor) though NAPA Echlin is a good choice. Stay away from the others. Oil pressure seems a bit low also. May want to put a mechanical gauge on it. The oil pressure senders fail all the time. Sometimes they fail and the dash gauge is pegged at 80 and other times they just read low. Or your engine is worn. 20 or more is more appropriate for hot idle.
Thanks very much for the post. I will have to check or replace the sending unit to see if that fixes the issue.

I believe the oil in it is 5-30, so maybe move to a 10-40 and see if the oil pressure is in a better range? Motor has 183k on it.
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Old July 3rd, 2014, 17:59
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Re: So bad temp sender?

Temp sending unit is proably faulty. About 210* on the dash gauge is normal.

10-15 psi at warm idle, and 35+ psi at 55 mph is normal. Most Jeep 4.0 L run about 40-45 psi at 55 mph.
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Old July 3rd, 2014, 21:35
Jaren1 Jaren1 is offline
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Re: So bad temp sender?

Quote:
Originally Posted by Tim_MN View Post
Temp sending unit is proably faulty. About 210* on the dash gauge is normal.

10-15 psi at warm idle, and 35+ psi at 55 mph is normal. Most Jeep 4.0 L run about 40-45 psi at 55 mph.
It is possible I have a bad oil pressure deal too, it seems to fluctuate at idle between 12-19 psi, I can sit there any watch the needle move around. On the highway it sits at about 39 psi just cruising at 50. Cold (85 degrees, sitting for an hour or so) it is at around 40 psi till it warms up.
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Old July 4th, 2014, 00:21
md21722 md21722 is offline
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Re: So bad temp sender?

If you and the previous owners have kept up on oil changes you shouldn't need thicker oil.

The bottom ends on these go on forever.

I have over 300K on mine and oil pressure hasn't changed since I bought it at 36K.
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Old July 4th, 2014, 00:55
Jaren1 Jaren1 is offline
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Re: So bad temp sender?

Quote:
Originally Posted by md21722 View Post
If you and the previous owners have kept up on oil changes you shouldn't need thicker oil.

The bottom ends on these go on forever.

I have over 300K on mine and oil pressure hasn't changed since I bought it at 36K.
I can only speculate on how the previous owner treated the car, Aside from never waxing it all seems to point to them taking normal care of the car. Im thinking its the pressure sender that is wonky since it will just move around at a parked idle with AC and everything else off. It doesnt make any noises and the motor is really actually quiet. Im going to get a mechanical gauge on Saturday to see whats up for sure.


So did we decide the temp sender is what is wrong with my temps since the rad hose and tstat housing both read at or around normal levels?
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Old July 4th, 2014, 05:50
djgrayxj djgrayxj is offline
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Re: So bad temp sender?

Note from DJ
Have a look at this post it has the Coolant Temperature Sensor resistance values that you need to check yours.
1997 Coolant Temperature Sensor Testing information
http://www.cherokeeforum.com/f2/cool...esting-188821/
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Old July 4th, 2014, 06:19
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Re: So bad temp sender?

A new temp sender is about $15-20, I would just buy one. About *210 at the thermostat housing is normal.

Oil pressure senders are about $20-25, if you think the current is funky, replace it. 10-15 psi at warm idle, and 35+ psi at 55 mph oil pressure is normal. Most Jeep 4.0 L run about 40-45 psi at 55 mph
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Quote:
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Old July 5th, 2014, 12:49
Jaren1 Jaren1 is offline
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Re: So bad temp sender?

Alright a little update. I went to napa and bought a mechanical oil pressure gauge and hooked it up. Turned it on an it read around 28 psi on what I would say is a warm idle, settled at around 26 psi or so. No fluctuations at idle, kept solid. Rose accordingly when throttle was applied to about 50 psi or so. Let it idle for about 8 minutes or so. Then I noticed that the temp gauge in the dash was reading correctly too, was sitting at just below 210 degrees on the gauge, so Im not sure what made it all of a sudden start functioning properly.

Just before I shut down the motor the mechanical gauge was hanging steady at just above 25 psi. Turned it off, hooked up the old sender and started the motor again, the gauge in the dash barely reached 20 psi and then the needle fluctuated constantly and dipped to as low as 10 psi. So its looking like thats my issue, which is a relief.
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  #11  
Old July 6th, 2014, 02:45
Dragonslayer Dragonslayer is offline
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Re: So bad temp sender?

A few years ago the temp gauge on my XJ went dead. Jiggling the wire harness
connector at the sender would bring the gauge back to life, but the gauge would
continue to drop dead or read low occasionally.

Cleaning the wire harness connector thoroughly with electronic contact cleaner
and a cotton swab fixed it more permanently.
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