Hey All, I have a 96' XJ with a problem I need some help with. I bought this about 100,000 miles ago and noticed the previous owner did some....lets call it specialty work on the temp reader. For whatever reason he cut the tube between the radiator and heatercore and put in a new sensor, about a week ago my temp gauge stopped working. No movement, its not a bad sensor as many bad sensors would max the gauge out before resetting back to the left, I recently cleaned the hardware of the sensor but quickly realized im in over my head as that did nothing and this involved some wire work. Any general advice will be appreciated.
below is the previous owners work; The sensor and the splice where it ends.

 

All single wire sensors work the same...the primary wire carries some voltage (X) from the gauge to the primary terminal on the sensor....the sensor has a resistive material that changes its resistance based upon the sensor temperature. The threaded base is the ground and is usually threaded into the metallic block or head and thus grounded..your sensor appears to have no ground wire. If it broke off, thats why it stopped working. If it did not have a ground wire it never worked

 

Thank you for the help, Ill ground the wire and if that doesn't work Im gonna replace the temp sending unit, Thanks again as I didn't even consider this needing to be grounded.

 

The simplest way is to wire brush the big hex so its mostly clean, clamp a wire to it with a hose clamp and secure it to the negative battery terminal. Are you using your factory gauge? If so, unless your new sensor has the same resistance curve as the stock sensor ...it won't be accurate.....here is the big question, is your 96 obd1 or 2. Early 96 had the sensor on back drivers side of the head....only worked gauge. Late 96 used the sensor in the thermostat housing and that fed the computer and computer drove the gauge

 

Talked to the old owner, apparently The engine is from a 98 so The parts I ordered wont fit and I need to return, the good news though, I grounded the wire and the sensor IS receiving signal, only now that, at all times, its reading off the charts; That resistance curve you mentioned. Need to find something with more resistance To lessen the signal I assume. For the moment Im gonna buy an IR reader with the money of those returned parts.

 

Then your temp signal comes off the computer, driven by the sensor in the thermostat housing. If your sensor or wiring is bad then you have a check engine light....unless the p/o removed the bulbs. Do you have a code reader...you can get the temps from the read data page

 

I still have all my bulbs, thankfully she doesn't have a check engine light but I don't have a code reader either, Ill get one and learn to mess with it and report back.

 

Did the PO only replace the block (long or short)? You still have the '96 systems (fuel, Ignition, PCM etc.)? The '97+ heads don't have the hole in the head for the sensor because the PCM drives the temp gauge. The '96 still relies on the sensor direct to the gauge. Since the hole's not there, the PO opted to install one in an adapter on the heater hose.

You said it's worked for a long time like this and suddenly stopped. What's odd is that it appears to have no ground connection.

 

You don't understand....if your truck is a 96, and your engine is a 98... the head is probably not drilled to accept the temp gauge sender at rear drivers side of the head. Thus the alternate sender. Since 96 it could be obd 1 OR 2. Obd 1 will not talk to a code reader. If you get the stock coolant temp sensor it will have the correct resistance curve, but its a 1/8 pipe thread. If you get several bushings and adapters, you can make it fit where your useless sender is now but you will have to wrap each one in teflon pipe tape

 

You said the gauge is now reading off-scale...High or low? Offscale high means shorted wire or sender and off scale low means open or extremely high resistance

 

I forgot to ask earlier...if you disconnect the wire off the sensor...what is the resistance from the center post to anywhere on the brass case or hex