Coolant temperature gauge

[WV Mike]

I replaced my oil pressure switch today. Yeah, my oil pressure is reading correctly. However, since doing so, I noticed my temperature gauge is stuck at about 1 o'clock position on the gauge. Any thoughts as to if I have to take the dash apart to get the temperature gauge to work again. I disconnected the battery in hopes that would get it to drop back down, but no luck.

[Fierofool]

Make sure it's securely plugged onto the sending unit.  Due to the location on the corner of the head, the connector can crumble.  If you only have the wires remaining, it's possible they're touching or swapped locations.  Slap the top of the instrument panel with the flat of your hand.  Works for dislodging the fuel gauge, so it should work for the temp gauge, too. 

[GTRS Fiero]

Mine has a different issue.  After driving about 300 miles, I made a rest stop, because the temp was showing about halfway into the red.  Nothing odd with vehicle performance, though.  Anyway, the coolant in the overflow tank may be a bit low, but otherwise everything looked OK.  I left the decklid open for a while, then turned the key 2 clicks.  The temp gauge read just below halfway, then started moving around.  Up and down, eventually going to the red, then back down to just below 220.

Bad gauge?

[Fierofool]

I would suspect the sending unit if the gauge sits at 100 when it's at ambient temp with ignition ON. 

[GTRS Fiero]

It sits at 100 with the ignition off, and the key out.

The temp light never comes on.

[Fierofool]

Though the gauge and light share the same sensor, they are completely separate.  The gauge circuit is a potentiometer.  The light circuit is an on-off switch.  One can work if the other has failed.  With cold engine and ignition OFF, key out, the needle should sit on the very bottom of the thermometer symbol.  That's why it's indicating a much higher temperature but still isn't boiling  You can remove the pod and without power applied, remove the needle and reposition it to point at the bottom of the thermometer symbol. 

Once you've reinstalled it, drive the car until it's up to operating temp.  Park it, leave the engine running and the AC turned off.  Observe the needle position when the cooling fan turns on.  For stock thermostat and fan switch, you should be at about 235*.  For Rodney's low temp fan switch and stock thermostat, the fan should come on at about 220*.