05 Montana temp gauge swung to fuel side!

[coghlan]

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 170F.

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)?

[formula1]

I would pay no attention to the position of a gauge when the ignition switch is off. Sometimes they stay where they were, sometime the needles drift with the power off. Either way, the people that designed the gauge system wouldn't guarantee that any reading is correct with the power off, so don't pay any attention to them.

What you are probably seeing is GM's double-coil gauge design. When unpowered, the gauge needles typically stay where they are, or stay about 1/2 way. Many other manufacturers use a single coil design and when unpowered, the needle drops to zero.

[rockwood84]

was the radiator hot or could you hear bubbling in the resavoir tank. if not could be bad temp sensor which is making it read hot when it is not.

[coghlan]

Now my gauges look like this: http://web.ncf.ca/ff293/Images/Tach.png

I don't think the engine is overheating...and I just filled the tank yesterday.

Is this a problem with sensors, the computer or the instrument panel?