Just replaced the temp sending unit on my '96 XJ (it's located on the rear of the head in my model). Thought the old one might have been giving me a false reading, but the new one shows temps almost in the red shortly after start-up. I know the thing is not getting that hot that quick. I was sure to order the one which is meant for the temp gauge and not the light. Maybe I got shipped the wrong part? Anyone else ever had this problem?

 

Check the ground from your engine block to the negative terminal of your battery. Check all other grounds for that matter. Bad sensor readings are often from a bad connection.

 

There is no ground wire for the temp sender.The sender itself is the ground.It's a one wire unit.Try putting di-electric grease in the harness,it will give you a good connection.If that don't work then try another one.The new one may be bad.Go to Advance,they are $9.99 there and I've had no prblems with mine.

 

Right, and the engine block has to be well grounded for the ECU to pick up the resistance of ground from the engine block to the sensor. Or in this case the gauge in the dash, rather than the ECU. The sending unit for the gauge in the dash is a variable resistor dependent on the temp of the coolant in the cylinder head. The coolant temperature sending unit which the computer uses to control fan speed and fuel mixture is a two-wire connection.

 

On the 96s the temp sending unit is a one wire unit not a 2.At least on my 96 it is.

 

the sending unit has nothing to do with gauge. you needed the coolant temp. senser at the front of motor in front of tstat. try this for location
Coolant Temperature Sensor (CTS) Resistor Trick

 

I see you have a 96 also.Disconnect the temp sender on yours and you will see it don't read the temp.Thats all it does is read the temp for the gauge and nothing else.

 

The one in the back is for the gauge. Yes they may have sent you the wrong one. How does your coolant look? Have you done the obvious? TStat etc? When I swapped clusters the idiot light switch was still in it and the gauge pegged out.

 

Yeah, I changed the stat, water pump, flushed and burped the cooling system. A mechanic said my radiator looks fine, but I'm starting to wonder.

Here's another thing... The new sending unit's nut is wider than the old one. When I put it in, it almost rubs against the valve cover... really a pain to get screwed in. I don't guess the valve cover could be heating the upper portion of the sending unit in a way that makes it read too high could it? (Anything is possible by this point I guess)

 

I bought mine at Autozone. Its made by Standard. Part number is TS334. Theres also another number on the box M10075. YES they are a PITA to get to! I doubt the valve cover would do anything. Is the wire connector black or white? The one for idiot lights are black. Gauges White. I had to do my gauge swap by learning. So thats why when I plugged the gauges in with the idiot light switch the temp spiked to max. When in doubt have the radiator rodded. Ive seen water pumps practicaly missing impellers too.

 

Yep, that's the exact part I bought. I have no clue how to remedy this gauge issue. (This whole job started after my water pump blew out about a month ago... overheating ever since. I've triple-checked my work to be sure it was done correctly). I guess the next step is to do a compression test on the cylinders to see if it's the head or gasket. If that checks out alright, I'll probably get a new 2 core rad.

 

Glad I saw this thread. I just bought an aftermarket gauge to replace my dummy light. I would have completely removed the wrong thing thinking it was the temp sending unit. You said it was at the back of the block close to the valve cover. I was like "wait...no it's not" Then sadly I found it way back there. lol.

 

I hope you can get to the problem. When in doubt take the T stat out and Quadruple the flushing. Good Luck! I flushed mine 6 times. The head could have gunk in it. Trust me it happens

 

Anyone have luck finding a new harness? Mine was fried/burnt to a crisp and the wire fell off. Having trouble locating a new harness. Has anyone jerry rigged one?

 

Haven't we covered this somewhere else?

That wire is part of a huge harness. Need to get creative.