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Temp Sensor/Gauge gone bad?
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JeepFever View Drop Down
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    Posted: 28 Nov. 2015 at 5:37am

Can a mechanical temp sensor go bad?

 
The needle does not move.  :(   . . . at first I thought maybe the radiator was low on coolant,  but it is fine.   I first noticed while splitting wood with PTO driven splitter a few days ago - > that the temp was not going up to normal 180.   I assumed it was just not getting warm enough at idle.   But today drove approx 15 miles,  and still no movement on needle.
 
The braided steel line from dash gauge to engine sensor looks fine.   I can "see" no reason it should not function correctly.
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Ryan_M View Drop Down
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It may be that your thermostat is bad. To test your temp gauge, remove the sensor and put it in a pan of hot water. Depending on your set-up it's probably easiest to remove entire assembly from the Jeep and then set it on the counter next to a pot of water heating on the stove. I know my wife loves it when I commandeer the kitchen to cook Jeep parts!
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Yes, gauges can go bad, as can the sensors. Are your radiator hoses getting warm/hot? Place a thermometer in the radiator to confirm coolant temp. Purchase a infrared thermometer and you can check the temperature of the block.

If your thermostat was stuck open I would think you would still get movement on your gauge. I suspect either the gauge or sender has gone bad.
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  There really isn't a "gauge" and a "sender", separate, in this case as there is in the case of an electrical gauge. It's all one unit, the "gauge". The "sensor", or bulb, is filled with ether (usually)or some other fluid, as is the tube leading from it to the gauge head, and the bourdon tube in the gauge. As the ether warms, it expands, creating pressure in the line and bourdon tube, straightening the bourdon tube and moving the needle. Any tiny leak will allow the ether to escape, and the gauge will stop working. Unlike letting the smoke out of wires, you won't see it. Wink  BW
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Originally posted by Red Willy Red Willy wrote:


If your thermostat was stuck open I would think you would still get movement on your gauge. I suspect either the gauge or sender has gone bad.

I just went through this about a week ago. No movement on my temp gauge so I replaced it. No movement on the new gauge either...hmmm....turns out the thermostat was completely shot. Replaced it and both temp gauges, new and old, now work as they should. I was surprised as, like you, thought a stuck thermostat would still allow it to warm up enough to get some type of reading but it did not.


Edited by Ryan_M - 28 Nov. 2015 at 6:08pm
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Thanks guys for some great input.
I did not even consider the thermostat,  but in my case I do not think that is the culprit, I must have a defective gauge assembly.  (I don't see any damage to the tubing,  but maybe it leaked somewhere)
 
Test:  cold engine . .   removed radiator cap and started engine . .  no movement of coolant visible in radiator when cold. .  after several minutes,  there was some movement of coolant in radiator  . . . a short time later - > the upper radiator hose got hot . .   the thermostat housing was hot to touch,  BUT -> the needle on temp gauge had not moved at all.
 
Looks like I am in market for an original-looking temp gauge,   any suggestions?  Smile
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This one from Walcks is nice.

http://walcks4wd.shopgate.com/item/383930
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I used that Walck gage with good success.  Checked it in boiling water and it was spot on.  Looks great too.
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There is a post somewhere on the forum or in the FAQ's that describes repairing these. It sounded  a bit involved if I remember.
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.
Yep,   a defective gauge in my case.     I borrowed a gauge from my '3A project,  and it works fine.   The thermostat seems to be working ok.
 
I thought it might be fun to repair the original,  but after seeing what is involved,  I think I will pass.  LOL
  a few links:
I like the looks of that Walcks "7:00 - 5:00" gauge,  and will probably get that one for replacement when the '3A project gets to the point of needing one.
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