Coolant Temp Sending Unit - to dash/gauge (not computer) - JeepForum.com

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post #1 of 17 Old 07-10-2011, 08:37 AM Thread Starter
Oxenhandler
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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).

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post #2 of 17 Old 07-10-2011, 09:03 AM Thread Starter
Oxenhandler
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It is hard to see and harder still to change out because there is so little clearance above and beside it, add to that, that the sensor itself is extremely fragile and easy to break.

Here’s another view of the temp sending unit in place. It is white. (b)
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post #3 of 17 Old 07-10-2011, 09:11 AM Thread Starter
Oxenhandler
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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)
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post #4 of 17 Old 07-10-2011, 09:18 AM Thread Starter
Oxenhandler
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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)
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Duralast Part No. TU236 Temp Switch.JPG  
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post #5 of 17 Old 07-10-2011, 09:25 AM Thread Starter
Oxenhandler
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Here's what the sending unit port looks like with the brass shaft/tube and brass threads of the sensor imbedded in it. (e)
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post #6 of 17 Old 07-10-2011, 09:27 AM Thread Starter
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To extract it I used a 7/16" screw extractor (f)
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Temp Sender (8).JPG  
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post #7 of 17 Old 07-10-2011, 09:29 AM Thread Starter
Oxenhandler
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I tapped the tip of the extractor into the hollow tube of the sending unit and turned it with a wrench. It was difficult as the swing room for the wrench was only an inch or two. (g)
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post #8 of 17 Old 07-10-2011, 09:31 AM Thread Starter
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But I did get it out. (h)
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post #9 of 17 Old 07-10-2011, 09:39 AM Thread Starter
Oxenhandler
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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)
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Temp Sender (10).JPG  
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post #10 of 17 Old 07-10-2011, 09:49 AM Thread Starter
Oxenhandler
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Here's the sending unit and the brass shaft that was once part of it (with the screw extractor still inside it). Ever wonder what's inside the temp sender? A steel spring inside a paper tube. (j)
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Temp Sender (16).JPG  
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post #11 of 17 Old 07-10-2011, 09:56 AM Thread Starter
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The End
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post #12 of 17 Old 07-10-2011, 04:43 PM
TheHalfWit
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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.

Calm. C.

If a week goes by without needing to replace something, pinch me because I must be dreaming.
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post #13 of 17 Old 07-30-2011, 05:26 PM
JeeperV8
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If this sensor is bad what will happen?
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post #14 of 17 Old 07-31-2011, 06:44 AM Thread Starter
Oxenhandler
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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.
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post #15 of 17 Old 07-31-2011, 08:49 AM
JeeperV8
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Got ya, how do you know when the sensor hours bad on you
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