False (red line) reading on 05 Montana temp guage?

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About 2 hours into a 3-hour drive I noticed the temp gauge up at the start of the red zone just under 125F. Twenty minutes before, I'm sure it was below the half way mark (100F).
I tried slowing to 60 mph from 75 for a few minutes, but it remained there. We had to pull over, and tried idling for a while, but it didn't move.
Finally, I turned of the engine, and the needle swung WAY to the left near the gas pump icon (10 o'clock)! This would be the equivalent of about 180F.
Every 5 minutes I turned the key to the ON position, but didn't start it. Each time I did this, the needle moved down the equivalent of 5 minutes on a clock. I also noticed that with the key in the OFF position, the needle didn't drop to the bottom of the gauge, but was moving lower each time. After 15 minutes, the needle pointed to 100F with the key in ON, and dropped to the bottom with the key in OFF. I started the engine, and everything looked fine for the remainder of the trip.
Is this some kind of computer glitch, in which the baseline temperature goes screwy (since the needle stayed at the halfway point on the gauge with the key on OFF)?
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> </head> <body bgcolor="#ffffcc" text="#000000"> About 2 hours into a 3-hour drive I noticed the temp gauge up at the start of the red zone just under 125F. Twenty minutes before, I'm sure it was below the half way mark (100F).<br> <br> I tried slowing to 60 mph from 75 for a few minutes, but it remained there. We had to pull over, and tried idling for a while, but it didn't move.<br> <br> Finally, I turned of the engine, and the needle swung WAY to the left near the gas pump icon (10 o'clock)! This would be the equivalent of about 180F.<br> <br> Every 5 minutes I turned the key to the ON position, but didn't start it. Each time I did this, the needle moved down the equivalent of 5 minutes on a clock. I also noticed that with the key in the OFF position, the needle didn't drop to the bottom of the gauge, but was moving lower each time. After 15 minutes, the needle pointed to 100F with the key in ON, and dropped to the bottom with the key in OFF. I started the engine, and everything looked fine for the remainder of the trip.<br> <br> Is this some kind of computer glitch, in which the baseline temperature goes screwy (since the needle stayed at the halfway point on the gauge with the key on OFF)? </body> </html>
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Red zone at 125F? Maybe 125C?

Could be, could also be the sending unit. Had that problem on one of my cars.
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Edwin Pawlowski wrote:

type="cite"> <blockquote type="cite"> <pre wrap="">Is this some kind of computer glitch, in which the baseline temperature goes screwy (since the needle stayed at the halfway point on the gauge with the key on OFF)? </pre> </blockquote> <pre wrap=""><!----> Could be, could also be the sending unit. Had that problem on one of my cars. </pre> </blockquote> The funny thing is that the return-to-zero point drifted down towards normal every time I turned the key to ON and back to off, finally reaching true bottom after about 15-20 minutes.&nbsp; Until then, it "floated" in the middle of the gauge when the key was moved to OFF.<br> </body> </html>
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