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Hi!

I'm new here and am not sure if starting a new threat is appropriate, so let me know if this needs to go somewhere else and I move it :) I didn't find an answer for this question in the forum, put plz apologize if I just was blind and didn't see it.

I just bought a 1992 Jeep Wrangler YJ (2.5/4Cyl) and replaced the upper radiator hose. I "burped" the system and everything. First time doing it, but it seemingly has worked well :)

BUT: Now my temp gauge is not working anymore. First it did not rise above the first line, now it is not rising at all anymore.

I also saw today that the radiator hose was slightly leaking and fixed that, by re-tightening. But I think it did not leak before today (I took the car on a drive yesterday). By all indication the temperature of the engine does at least not get too high. Also, the radiator hose does not get hot immediately (bc of that I am thinking that the thermostat is at least not stuck in the open position).

My suspicion is that it's either the sending unit to the gauge or some wiring issue. Or maybe the fuse blew? Not sure. Or is it the thermostat after all? My question: how do I go best about diagnosing what is at fault? How do I rule out that it's the thermostat, and it is indeed the gauge that is faulty? I don't want to replace the thermostat or sending unit if I don't have to :D :D :D

Thank you all for your help in advance! :)
 

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Welcome to the Forum leoMB,

The temp sending unit works by providing a variable ground to the gauge. If you used Teflon tape, it probably is preventing the ground to occur.
Remove sending unit and remove Teflon tape. Reinstall the sending unit. Use a conductive sealant if you feel the need to seal the threads.

Good Luck, L.M.
 
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If the gauge doesn't show any signal at all, check the connection as L.M. suggested, I would add to check the wiring back to the harness for burned or broken continuity evidence, after that its a long piece of wire from the plug to the gauge to check for shorts with a VOM.
 
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Discussion Starter #5
Thanks all! I will burp it again first, in the hopes a air bubble got caught at the sensor :D Then I'll go and try to find the cables for my VOM and get started on the search for faulty wiring!

Thanks again! I already love this forum :)
 

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Your sensor reads temp with or without coolant touching it. While I would not dismiss the need to get the air out of the system, your gauge issue is an electrical one.
 

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This^

Also you don't have to burp anything... just drive it and keep topping off as needed.... the engine will burp itself while you are driving just like you do after spaghetti night...

You can verify thermostat function with an ir thermometer or can at least verify it's close (enough that your gauge should have moved) w your hand... 195° is too hot to hold on to so of you can keep your hand on the thermostat housing then the engine isn't at proper temperature.... 100° feels like bath water and 150 feels like hot tap water...
 

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Oh, okay! Thanks! I'll burp it in case there is still air in it and will turn to the electrical troubles as well then! I'll let y'all know the outcome of my endeavors.
 

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^What He said!, You can Idle that thing all day long and not get the air all out until you get the engine up to operating temp and enough RPM's on the pump to move the water completely through the system
 

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Alright, so as you will begin to realize —*I am absolutely new to electronics in cars :D

As I was about to inspect the wiring of the sending unit itself, I found an unplugged wire hanging out there? And there is only one individual wire coming out of the sending unit, too.

I made a video to show you.

What is that unconnected black wire (can you tell from the video?). You should see where it is coming out. I assume that this one individual blue wire comes out of the sensor is correct?

As you see: I am just beginning to learn all of this, so really: thanks for the input and guidance.
 

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Find a post by Got it at last. (Above post^^^) In his signature there's a free link to several Factory Service manuals and a couple Factory Parts Manuals.
Open that link and click on the manual that you need. The schematics are in the electrical troubleshooting section.

Good Luck, L.M.
 
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Alright. So I figured it out (partially) and wanted to report back.

I THINK, the issue is: There is only one wire coming from the CTS. Oddly enough, there is no other wire (the black one seen in the video I posted above runs to nowhere) so I gonna next open up the gauge panel and see what wire is running where.

I did not yet test the sensor itself, as I want to hold off training and removing it for as long as possible, especially as the highs are in the mid to high teens outside right now :D

The good news is: the engine seems to be running on a good temperature. The radiator hose does not immediately warm up, while the hose running to the back does, telling me that the thermostat is not shut open. And the hose does warm up after a couple of miles driving —*so that tells me that the engine is getting hot enough for thermostat to open/and the thermostat is working properly.

So now all I got to do is figure out that darn wire, which I suspect is the faulty part. Cross your fingers, you wonderful people!
 

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Discussion Starter #13
Edit: drain, not train. Drain the coolant in order to remove the sensor. I am not intending to train anything right now, way to busy trying to figure this whole car thing out :D .
 

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It definitely is an electronic issue. Mine behaved the same way and it was simply because the wire plug had been nudged off of the little sensor screw on the back of the block. If you’re sure of that connection it is probably the other end of the wire or a short inline somewhere. Also, clean the copper on the back of the gauges. It could be corroded, preventing reliable signal.


Sent from my iPhone using Tapatalk Pro
 

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Thank you so much dsaylor! I'm pretty sure it's that. There is only one cable coming off the sending unit. I just can't see where the other cable would be, it's oddly wired. I'll post a photo of the situation tomorrow, in case I can't figure it out —*maybe someone here can make sense of it :D

Also doing my first all-alone serpentine belt replacement tomorrow!
 

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Fwiw you don't have to drain anything to change the sender.... just have the new one ready and swap them on a cold engine... you'll lose an ounce or so of coolant at most....

You can test the wiring and gauge by simply removing the wire from the sensor... turn on the ign and the gauge should swing all the way to one side... then ground the wire and the gauge should swing all the way to the other side...

If it does that then the sensor is your problem...
 
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