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Temperature Gauge Pegged Hot


Schon '02

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After a short drive, The temperature gauge is pegged in the red. The two upper hoses are hot; the lower hose is cool. Bad thermostat or bad gauge?

 

Im pretty sure it’s the thermostat, but waiting for the car to cool down to see if the gauge reading changes. 

 

 

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Thanks. Easy once I get the car home. Having lunch while the car cools off. If the gauge still

pegs after a reasonable cool down then I’ll proceed home cautiously assuming it’s a bad temp sensor or instrument gauge ground. 

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On my car that I recently bought had the same problem. With my situation I found no coolant flowing thru the engine block. I removed the engine coolant plug and nothing came out. Told a wire hanger and starting poking and fishing out the years of crud that was built up in the gallies. I ran a hose in the radiator and flushed out the mess until I got a free flowing system. Driving at all speeds the temp gauge stays right at the half way point. Check it out and hopefully this tip will help. Let us know. 

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Another possible reason (if your thermostat is ok)...............I had a similar problem years ago. A hefty thump on top of the dash/gauge cluster & it dropped to show the correct temp. Next bump & back it went up into the red. Putting the famous earth lead directly onto the back of the gauge cluster fixed it.

Les

'74 '02 - Jade Touring (RHD)

'76 '02 - Delk's "Da Beater"

FAQ Member #17

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Huh.

My solution was always to take the flat palm of my hand and give the binnacle a good whack, sometimes it took two or three.

 

Check the grounds on your car, and the extra ground wire fix for gauges.....IIRC there is a post here on the FAQ, or may be Mike has a Tech paper....

 

It was never the thermostat as evidenced by the testing procedure above....and annual flushing and coolant.

 

:)

 

 

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29 minutes ago, 02Les said:

Another possible reason (if your thermostat is ok)...............I had a similar problem years ago. A hefty thump on top of the dash/gauge cluster & it dropped to show the correct temp. Next bump & back it went up into the red. Putting the famous earth lead directly onto the back of the gauge cluster fixed it.

 

This is a good point. Even when overheating dramatically the car will take a couple of minutes to get up there. Any gauge needle movements within a couple of seconds (or even near instantaneously!) is suspect and probably an electrical issue or, as Les points out, a mechanical issue with the gauge. I have one of these too where my temp gauge stays pegged at the bottom if I haven’t driven for a few days. A hefty whack on the dash frees it up and it springs to attention. 

Edited by Simeon

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Thanks for the input. After lunch, and with the car cooled down a bit (radiator and hoses warm to the touch), everything was normal (coolant level, engine start up, idle, no visible leaks...). But the Temp gauge immediately pegged out to max when the ignition key was turned to the “on” position. The gauge zeroed when the temp sensor wire was pulled. So the gauge was behaving as if the sender wire was grounded (which is an indicator of a bad sender), and the decision was made to make the drive. Had there been any other signs of overheating such as coolant boiling or excessive overflow, we would have called for a tow. We made the 70 mile trip back no worse for wear, and if the grounds check out, a new sender will be ordered.

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It's unusual for the temp sender to fail (mine are both original); a poorly grounding gauge is usually the culprit.  Try this--first drain off some coolant to get the level below that of the sender, then remove it and clean the threads thoroughly with a stainless steel "toothbrush."  Then do the same with the threads in the water manifold, and the male and female terminals on the sender and wire respectively.  Reinstall and see if that makes a difference.  Don't forget to replace the coolant you drained!

 

The brass sender housing and aluminum water manifold cause dissimilar metal corrosion and can bollix the electrical circuit as the sender grounds through its threads.  

 

mike

Edited by mike
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  • 1 month later...

Update... The root cause for the temp gauge pegging was a bad ground.

 

The thermostat checked out with a hand held IR gauge

verifying all operating temperatures within normal parameters; the temperature gauge sender was replaced and the symptoms continued; the instrument cluster had a ground wire connecting both gauge screw posts on the back side, and the addition of a ground wire from the posts to the body made no difference. So, the only thing left was to chase the problem back to the gauge.

 

Removing and opening the instrument cluster revealed the gauge ground connector hanging on to the edge of circuit board tab solely by the wire tension. It was never fully pushed onto the tab. Making matters worse, the screw post was loose and had pulled out of the back side of the gauge case when I previously checked and tightened the knurled secruring nut. 

 

All is is now fixed and working as it should.

9360AFA0-9903-4F09-BC8A-1B61A19F532B.jpeg

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  • 2 years later...

Well, let me add to this thread.  I DID have my temperature gauge working after it was pegged hot.  I added the instrument cluster ground and an additional engine ground (negative battery cable to driver side of engine compartment).  I had earlier checked out the temp gauge as noted above, and had performed the hot water / ohmmeter test on the temp sensor.  One of the above actions apparently corrected the problem, and all was fine for a few weeks and I have not driven the car at all.  Last weekend I had the motor running for a short while and the gauge was working fine.  Now, suddenly, its pegged again (while car is off, engine cold).  Any ideas?  I have ordered a new temp sensor...?

Edited by its55
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