Replacing Coolant Temp Sending Unit - to dash/gauge (not computer)
The change out described in this thread was on a 1995 Jeep Grand Cherokee, 6 cylinder, 4 liter engine, here known as a ZJ.
The 95 has two temp sensors, one in the front of the engine compartment, on the t stat for the computer and one on the back of the head for the dash. The one on the back of the head is the one to the gauge.
The 96-98 have the gauge run by the pcm (powertrain control module, aka, computer) with no need for a second sender.
Yesterday, TheHalfWit on this forum wrote and I paraphrase, "But the 93-95 4.0's have a second sender on the very back of the block, under the wiring for the injectors, 3" from the firewall and it is a ***** to change."
Here's where you'll find the temp sensor/sending unit/switch for the gauge, follow the orange arrow (a).
The factory original stopped working. It was broken, probably snapped by a mechanic's tool during a tune-up. Removing it, I broke the white ceramic top completely off because I didn't have the deep socket tight against the nut when I cranked it. Here’s what I was left with, the shaft, the threads and the nut (c)
To replace it I bought a Duralast brand temp sending unit from Autozone, part number TU236 Temp Switch. But I over tightened it, installing it, and snapped off the white ceramic top AND the brass nut, leaving the brass shaft and threads imbedded in the engine.
Here you see the factory original with the white top snapped off, the Duralast brand with the brass shaft/tube broken off and the Duralast part box. (d)
I bought another sender, NAPA part No. TS6685 and installed it gently. Even so, I broke it. But not so much that it doesn't work. It works great!
The trick is not to over tighten as the nut and tube are thin, hollow, brass and not to crank on the ratchet unless you are certain the deep socket is all the way over the nut. The socket will twist the white part independent of the nut and break it if you do not have the socket all the way over the nut and the hollow, brass nut will twist off the hollow, brass threads if you over tighten.
Note: each of these senders required a different size deep socket, 11, 12 and 14mm.
Here you see the NAPA box, two broken senders, one intact sender (the one that's in my Jeep now!), and the screw extractor (i)
I know this isn't strictly related to the thread, but its a mistake I managed to do while I was changing the sensor.
That crooked hose is the PCV hose, and it looks like you knocked it loose like I did. The easiest way to check for that is just to listen for a hissing. In all likelihood you'll need a new grommet for it, so that it will seal up tight.
If a week goes by without needing to replace something, pinch me because I must be dreaming.
You won't be able to monitor your coolant temperature. So you won't know you're overheating until you see steam escaping from under your hood by which time it may be too late to prevent costly, repairable harm to your radiator and engine. For starters, your radiator may crack.