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Temp guage - drops

Apostle

Apostle

NAXJA Forum User
Location
COS
Started today, the temp guage would drop like the electric was off, but would jump back up. happened off and on. sometimes for a couple mins, sometimes for just a few seconds. happened when i put on the gas, happened when i was just cruising.

suggestions?
 
sounds like an intermittent connection. What year is your XJ? If it's RENIX I don't know for sure where the gauge temp sensor is, I think it's on the side or back of the head. If it's OBD I or a 96 I think it should be at the back of the head. If it's a 97+ I seem to recall there only being one temp sensor, since the gauge cluster is computer controlled, and it's the one on the thermostat housing.

All or some of this info may be blatantly incorrect... except for the intermittent connection bit. I'm quite certain that's what the problem is.
 
Always post the year/engine of your XJ for most accurate responses.

If the temp changes are INSTANTANEOUS, the most likely suspect is electrical as already mentioned.

If they happen over a short period of time, that changes the suspect list (stat, air pocket in coolant, etc).
 
97, 4.0

instantaneous. figured it was electrical, but not sure if behind the dash or at the sensor/sender/whatever. have a chilton, but its cold outside. looking for info before i dig into it.
 
Inspect wiring around the sending unit on the thermostat housing. If all looks good, I'd replace that sender.

Sending units fail way more frequently than gauges do.
 
Pull the plug off the temp sender on the thermostat housing and clean the contacts on the temp sender. Same thing happened to my buddy's 98...even got to the point one day where he started it up after changing the oil and while he was letting it run it spazzed out so much it made the e-fan come on and the motor shut off (threw a code at this time for the temp sender). After cleaning the contacts, no more problems.
 
Mine ('97) was doing that and it turned out to be a short to ground on one of the sensor wires at the back of the head. If it's an intermittent problem then it's probably not the sensor. Inspect the harness for rubbing and see if there's an issue.
 
Remove the wire from the sender.

Ground the wire and see if it pegs the gauge.

Drive it around with the gauge pegged. If the gauge suddenly drops you know the problem is an intermittent open in the circuit. If the gauge remains pegged, replace the sender and don't use a ton sealant--it grounds through the body to the head and too much sealant will screw up its readings.
 
Where is this thing? per the book it is suppose to be to the left rear of the engine. picture shows near the top. nothing back there
 
There was a 2 wire plug, plugged into the water pump (???) front of the engine. unplugged that but nothing happened, still showed temp
 
Apostle said:
Where is this thing? per the book it is suppose to be to the left rear of the engine. picture shows near the top. nothing back there
Click to expand...

OK--you have a 97. On 97 + my suggestion isn't going to work. You have a combination PCM coolant sensor and temperature gauge sender in the thermostat housing. The PCM controls the gauge if I understand the other posts I have read on NAXJA--new fangled doo-dads you young whippersnappers get yourselves mixed up with!

I would check with Winterbeater, Kastein, 5-90, ehall, Tim_MN, or BirchlakeXJ on your issue. Send one or all of them a PM.
 
The resistance values for the sensor across a range of temps have been posted on here before. A quick google didn't find them, but they're around. Someone may be nice and post the values from the FSM- if not, I'll try to find them later- I know I've got it around somewhere. I'd clean the contacts, and check the wiring where it's visible as a start- intermittent function would lead me to think it's a physical issue with the wiring/terminals.
 
I'm flattered that I made that list...

on a 97+ I'm not sure, I'll poke around in the parts catalog/FSM and see if I can find any info. You are right on the CCD bus bit for sure, the 97+ dash is mostly fed via that.

On a 96 down to sometime in the early 90s, it's a 1 wire sender at the back of the head.

EDIT: add MJR to that list, either he remembers way too much XJ tech or works at a dealership, I forget which.

EDIT2: from the 97 FSM -
The instrument cluster circuitry calculates the proper gauge pointer position based on an engine coolant temperature message received from the Powertrain Control Module (PCM) on the Chrysler Collision Detection (CCD) data bus. The PCM uses an input from the engine coolant temperature sensor and internal programming to decide what engine coolant temperature message is required. The PCM then sends the proper message to the instrument cluster on the CCD data bus.

...

The engine coolant temperature sensor is installed in a threaded hole that penetrates a coolant passage of the engine. Refer to Group 14 - Fuel Systems for more information on the PCM and the coolant temperature sensor.
Click to expand...

Group 14-42 has an illustration showing the CTS to be on the thermostat housing, so I think it's all the same sensor on a 97+.
 
Last edited:
The sensor is in the T stat housing on all 97+.

Here's the table- I think this is for both the CTS and IAT?
http://i266.photobucket.com/albums/ii244/AHhub/forum stuff/Resistancetable.png

- I'm fairly certain this is from a FSM- if this violates the rules, delete the post please.

The harness, I'm guessing, goes to ground, and the PCM? Where would you check continuity on the wiring? One of the PCM connectors?
 
Last edited:
Looks exactly like the table in my FSM. However, I am pretty sure posting a snippet that size (and the size of the quote I posted) is well within fair use guidelines, so I'm pretty sure you are in the clear.
 
kastein said:
EDIT: add MJR to that list, either he remembers way too much XJ tech or works at a dealership, I forget which.
Click to expand...

When you hear MJR, just think JEEPGOD. It will be much easier.
 
In 2000 FSM, wiring diagram shows a tan/black wire going from the PCM to the temp sensor. Ground is through a brown/yellow wire going back to the PCM. That is a common sensor ground for many sensors. You could put a variable resistor in the plug in place of the temp sensor, adjust it to put the gage in the middle and drive it around a little to see if it still jumps around. You can also measure the resistance if your variable resistor (with an ohmmeter) at the temp points you want to compare in the resistance table. An old volume control from a radio or TV would work fine for a variable resistor.
 
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