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Temp Gauge woes (long)


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Recently the 94 XJ had to be towed back to my daughter's dorm - it had bled out all of its coolant (through a failed solder joint in the 1 year old radiator). After tearing into it, I found the thermostat was faulty also and the water pump impeller was loose on the shaft. Replaced:

 

Water Pump

Thermostat (195 degree)

Radiator

Upper and Lower Hoses (with spring!)

Thermostatic Fan Clutch

Radiator cap

 

Now, when she called me to report the failure, she indicated a large puddle of coolant was under the vehicle, and she had shut if off at the temp gauge in the red. When I opened up the block it was almost dry. :( Replaced parts, closed it up and noted the temp gauge is now acting strangely. When cold, the needle rests just above the 100 degree mark, and upon start it moves all the way to the red side, then back to 100... then slowly climbs to what appears to be 240...then falls back to below 210 momentarily before climbing back to 240.

 

Obviously, the momentary drop is when the thermostat opens, and when I hold the upper hose I can feel it happen, but the climb back to 240 after that bothers me (cause she's about a 5 hour drive away from dad). When the vehicle is fully warmed up I can still hold the hose in my hand...which makes me think there is no way it could be 240 degrees in there.

 

Replaced the temp sender for the gauge 8 months ago (purchased from stealership).

 

So the questions:

Can the needle on the gauge be pushed out of accuracy when it bottoms out in the red zone? Can it be "reset"? (wouldn't bottming out in the red zone cause the needle to read low instead of high?)

 

I read Don's writeup on testing the gauge, but don't have the equipment to do it. Does anyone know of a place where you can get OEM temp gauges for the 94 XJ? (the 93 and younger gauges are not the same scale).

 

Thanks

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did you try burping it through the rear coolant sensor hole? (of course, I'm assuming that 94 XJs have one)
They do. Dash temp sensor is in the same place as Renix engines.

 

Yes and yes. However, I was always lead to believe with the open system that was not necessary.

 

The system seems to be operating as advertised, its just that the gauge doesn't match. With a little help I did locate a source for the replacement gauges, but I'm going to get a laser thermometer and confirm the component temps and thermostat opening temp first.

If all is accurate in the front I'll just replace the gauge.

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When mine was behaving similarly, it was because it had eaten a head gasket and had air in the system. My working theory was that the temp sensor was reading the air temp, and not the coolant, since I too could hold the hoses and the radiator. This wasn't immediately evident, of course, until I drove it home on a check ride and kept going when it pegged @ 265°F (I'm not normally

vindictive to my Jeeps, but when you've replaced the cts, the Rad, the thermostat, added a fan shroud, replaced the water pump, and the wanker is still overheating...) and it spit the head gasket out the back, where it had had a pinhole leak, I believe.

 

I'm fervently hoping that isn't your problem. Definitely burp it, repeatedly.

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