Temperature gauge randomly works. sometimes it works fine for a week or so then a week or so it will read hot some times the gauge will point to the r for reverse or neutral. when you shut the car off it will not go all the way to the left to set itself right. the temp always reads fine when on computer when the gauge is showing hot. the gauge and sensor has been changed.

SOURCE: 97 montana fuel gauge reading over full all the time

it is a sensor issue take it to a look dealer or a local mechanic and he can fix that for u

SOURCE: possible overheating, 2004 pontiac montana

Its definitly a bad reading, you would know if your vehicle is overheating, you can usually smell it right away.I would say its your temperature gauge sending unit is defective, check the wires to see if they are well connected or broken. ask a backyard mechanic for assistance.

SOURCE: Temperature gauge shows hot

head gasket does the overflow bootle have bubbles in it when idleing warm if does most likey rear head gasket.

Steve Allison

• 5569 Answers
• Posted on Jan 19, 2009

SOURCE: 2004 Bonneville - Temperature Gauge is Erratic

Since there is no voltage applied with the ignition off, if the gauge is not dropping down all the way, it is the gauge that has failed.
Temperature sensors are frequent failures but they are not active when the car isn't powered up. They can be intermittant, high, low but with no power, the gauge itself should go to the minimum.  

SOURCE: temperature gauge rises when idling

First check that your fans are operating and coolant level is full. If they are, check that there are no leaves etc stuck betweren the radiator and the AC condenser.Last option is a bit more expensive...radiator may be partially obstructed internally (would need flush or replacement)
Egg smell brings me to another potential problem if converter is partially plugged it will raise engine temp as well...the rubber smell is oil residue on block getting hotter than normal and evaporating.
If you work on this yourself ask any techinical questions you have along the way and I'll try to help. Otherwise get the car to a shop asap...overheating in any form can severely damage your engine.
Good luck!!