I've got a 96 cherokee classic factory 2wd, when i got the jeep it had a bad engine so i put a used 4.0 in it and the used one i put in doesn't have the second coolant sensor port for the guage on the head by the firewall. But my jeep harness Has the pigtail there for it, it also had the cluster with the dummy lights in it. I've done the cluster swap with guages and they all work but oil/coolant temp, I've narrowed the oil guage to a bad sensor. I did drill and tap the t-stat housing and put the second temp sensor ( 1 terminal) in and just extended the wire to reach it. But the guage still isn't working???

when key is off it goes to pegged cold when I turn key on it goes to pegged hot??

Any help will be appreciated, thanks!!

 

are the sensors touching?

 

They are close to each other but not touching

 

on my 1996, the coolant temp gauge sensor is on the back of the head....one wire connection. The thermostat housing sensor is connected to the PCM....what year was the replacement 4.0 you put in?

 

I don't think you are getting a ground for the sensor you added. As a test you could run a jumper from it to the negative battery post and then check its function. Where it was originally mounted it had a good ground in the head but I think the thermostat housing is more insulated with gaskets and goo to keep it from leaking!

BTW, I am in the same boat with my 96. Swapped out a bad engine/head for a good one but never tapped the thermostat housing to go the route you have. I have been limping along by using a Bluetooth sender in the OBD port and watching temps on my phone. A pain but a stop gap method of keeping tabs.

What size drill and tap did you use on your thermostat housing. I will be picking up my repaired heater core today and putting things back together. Might as well finish that job as well.

 

From the numbers stamped on the side of the block It's a 98

 

The drill bit I used was 21/64 metal bit, and the tap was 1/8-27 npt!

 

That was it, coolant sensor wasn't getting a good enough ground. Thanks bud!!

 

Glad I nailed it, the giveaway was it only has one wire so it had to ground through the threads.

A big thanks to you as well, you saved me a bunch of time by giving the drill bit and tap size!

Thanks!