sparton013
NAXJA Forum User
- Location
- Arizona
This is my first time posting so I apologize in advance if I left out any key pieces or information or if I provided way too much irrelevant info. I figure too much info is better than not enough.
1988 XJ Laredo – 4.0L 6cyl – 4x4 Auto Trans
I was driving my Jeep and all of a sudden the temperature gauge started going crazy. Fluctuating all over the place from normal operating temp then instantly pegging past the max and then back down to normal temp. I pulled over in to a parking lot and checked the engine bay. Nothing seemed out of the ordinary as far as the actual coolant system (closed, not open). I started the Jeep back up and the temperature gauge was stuck at max now. Luckily, I was only a couple miles from my house so I managed to drive it home OK. While on my way home I noticed whenever I would go over an overly-bumpy section of the road enough to really rattle the Jeep, the needle on the temp gauge would start to go back to reading the normal operating temp for just a split second before returning back to max.
The temperature gauge is stuck at max even when the engine is completely cold. It is also stuck at max when I turn the ignition switch to the ON and START positions. All other gauges in the instrument cluster work perfectly fine.
The first thing I did was replace the Coolant Temperature GAUGE Sending Unit located at the rear of the head on the driver’s side. The problem persisted. I unplugged the single purple wire that connects to the CTSU and the gauge is still stuck at max. I traced the wire from the CTSU all the way back to where it goes in through the firewall. The insulation is healthy with no signs of wear or exposed wire (in the engine bay).
This leads me to believe the problem lies somewhere in the wiring in the dash area. My problem is I don’t know how the temperature gauge is wired (without tearing apart my dash). Is it wired through the ignition switch in any way? Or does the wire connected to the CTSU go through the firewall and directly to the connector on the back of the instrument cluster? I’m very ignorant with diagnosing electrical connections and circuits which doesn’t make things any easier. But that’s all part of the learning process. It seems to me that there is possibly a spot where the wire might be contacting another source of metal and getting constant power?
Any advice is greatly appreciated. I intend on doing a full conversion of the cooling system from a CLOSED to an OPEN system before the upcoming summer season. But before I do that, I want to resolve my faulty temperature gauge.
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Some quick backstory to my Jeep… My parents bought this Jeep brand new from the dealer. It was used as my mother’s daily driver and never saw any off-road action. Sometime around 2003 it began having some transmission shifting issues that caused my parents to park the Jeep in our garage and drive other vehicles.
The Jeep sat for over 15 years before I began working to restore it to its former glory. I’ve done all the repairs and restoration myself. Funny enough, the transmission shifting problems were all a result of 1 wire that burned up and came loose from the connector going in to the Transmission Control Module (TCM or TCU) located under the passenger-side of the dash. A few dollars in new electrical connectors and terminals is all it took to get it working as intended, and not thousands of dollars to tear in to the transmission like the dealership originally quoted to my parents years ago.
I’ve done several other replacements of core components and old sensors. But currently the Jeep is still all OEM with the exception of the Rough Country 3 inch lift kit I installed.
I am aware of Cruiser54’s website for our older Renix Jeeps. The only tips I’ve done so far is cleaning some of the ground connections (oil dipstick tube stud, braided cable on firewall, starter relay connections) and completely removing the C101 connector.
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1988 XJ Laredo – 4.0L 6cyl – 4x4 Auto Trans
I was driving my Jeep and all of a sudden the temperature gauge started going crazy. Fluctuating all over the place from normal operating temp then instantly pegging past the max and then back down to normal temp. I pulled over in to a parking lot and checked the engine bay. Nothing seemed out of the ordinary as far as the actual coolant system (closed, not open). I started the Jeep back up and the temperature gauge was stuck at max now. Luckily, I was only a couple miles from my house so I managed to drive it home OK. While on my way home I noticed whenever I would go over an overly-bumpy section of the road enough to really rattle the Jeep, the needle on the temp gauge would start to go back to reading the normal operating temp for just a split second before returning back to max.
The temperature gauge is stuck at max even when the engine is completely cold. It is also stuck at max when I turn the ignition switch to the ON and START positions. All other gauges in the instrument cluster work perfectly fine.
The first thing I did was replace the Coolant Temperature GAUGE Sending Unit located at the rear of the head on the driver’s side. The problem persisted. I unplugged the single purple wire that connects to the CTSU and the gauge is still stuck at max. I traced the wire from the CTSU all the way back to where it goes in through the firewall. The insulation is healthy with no signs of wear or exposed wire (in the engine bay).
This leads me to believe the problem lies somewhere in the wiring in the dash area. My problem is I don’t know how the temperature gauge is wired (without tearing apart my dash). Is it wired through the ignition switch in any way? Or does the wire connected to the CTSU go through the firewall and directly to the connector on the back of the instrument cluster? I’m very ignorant with diagnosing electrical connections and circuits which doesn’t make things any easier. But that’s all part of the learning process. It seems to me that there is possibly a spot where the wire might be contacting another source of metal and getting constant power?
Any advice is greatly appreciated. I intend on doing a full conversion of the cooling system from a CLOSED to an OPEN system before the upcoming summer season. But before I do that, I want to resolve my faulty temperature gauge.
######################################################################
Some quick backstory to my Jeep… My parents bought this Jeep brand new from the dealer. It was used as my mother’s daily driver and never saw any off-road action. Sometime around 2003 it began having some transmission shifting issues that caused my parents to park the Jeep in our garage and drive other vehicles.
The Jeep sat for over 15 years before I began working to restore it to its former glory. I’ve done all the repairs and restoration myself. Funny enough, the transmission shifting problems were all a result of 1 wire that burned up and came loose from the connector going in to the Transmission Control Module (TCM or TCU) located under the passenger-side of the dash. A few dollars in new electrical connectors and terminals is all it took to get it working as intended, and not thousands of dollars to tear in to the transmission like the dealership originally quoted to my parents years ago.
I’ve done several other replacements of core components and old sensors. But currently the Jeep is still all OEM with the exception of the Rough Country 3 inch lift kit I installed.
I am aware of Cruiser54’s website for our older Renix Jeeps. The only tips I’ve done so far is cleaning some of the ground connections (oil dipstick tube stud, braided cable on firewall, starter relay connections) and completely removing the C101 connector.
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