My temperature gauge on my 92 Cav. is going from a cool temp, to a hot temp within seconds. What causes that?

If the cooling system is functional, yes.
The ac condenser adds heat to the air coming thru the radiator when the ac is on. If the engine cooling system is weak, the extra heat will make the engine run hot.
Low coolant flow thru the radiator is a common cause.

Air pockets will make the guage do that, and also cause your heat to come and go. Also, a poor radiator, as in rotting, or plugged up, will cause high temperature issues.

Air bubbles would not cause what you describe, the correct thing to do is to measure the temp with an external gauge. The sending unit is the usual cause, and pretty inexpensive to replace it, for diagnostic purposes...It is filled with wax and eventually fails....

The most likely cause is due to the radiator fan constantly running and the engine not getting to operating temperature, thats why your temp gauge isnt going up, check all related wiring to the cooling fan and make sure there no bare wires that could be causing a short to ground causing the fan to constantly run, secondly check the fan relay, if all of that checks out check the coolant temperature sensor because the information from that sensor tells the computer when to turn the fan on and off, if the sensor is bad it could be telling the computer the engine is hot when in fact its not.

There could be a number of causes of a fluctuating temperature gauge but most commonly is the thermostat. It could also be a head gasket, cooling fan problem or the actual temperature sending unit. I hope this helps!

Is the heater nice and hot when the needle shows low temp? If the cooling fans turn on and the heater is hot, that leads me to believe the coolant temperature sensor is bad. You should try replacing that sensor. They are only $6 usd here. As long as your check engine light is not on and your fans are running, this will not hurt your car... but this is something you should fix soon if you can. Make sure the engine is cold when you replace the sensor

the temperature sending unit on a 97 grand prix 3800 gt(which is also the coolant temperature sensor) is not accurate. the sending unit part of this sensor only sends info to the guage on the dash. the coolant sensor part sends info to the computer of the car. it is located under thermostat and somewhat difficult to get at. i had put a brand new one in and my temperature on my dash is all over the place---even with good thermostat and properly bled system. when i hook up a scanner to my computer, the coolant sensor is sending the computer(ecu??) what seems to be the right temp. anywhere from 194 degrees to 217 when hot. the guage however on dash go from 160 to 260 in less than 2 minutes.

Check to make sure your thermostat works right by monitoring the warming up of your engine. With a completely cold engine, start and run the engine for a few minutes, then put your hand on the top radiator hose to monitor if and when it gets warm as the thermostat opens more and more and note the gauge reading( if it works) the top radiator hose should be unbearably hot within 5-8 minutes. If the therm. opens right it should close right aswell, staying open a little while eventhough the radiator may have cooled may be what you are experiencing causing the rapid cooling and is nothing to worry about. The Hose should not get warm very soon after starting the engine. Regarding you gauge, lets take one step at a time, verify proper op. or the therm.

I have a 2002 Mitsubishi Montero Limited. The other day the temperature gauge went from normal temp to Max HOT. The radiator is still cool enough to touch, it is not boiling over, and there is still coolant in the resivour. The gauge would go back down to normal in a few minutes, but now it immediately climbs to Max Hot within 1-2 minutes of turning the car on.