Temperature gauge goes up then down engine

air lock in the cooling system get a plastic bottle cut the bottom off turn upside down put on radiator filler and run engine cut full off water wait until all air bubbles stop then remove and put cap on see how that goes

Best case scenario is your thermostat is stuck open. When this happens the engine will take a long time to warm up and will never get up to full temp. Worst case could be a serious problem such as a blown head gasket. If there is no coolent in the engine the temp gauge will not register either.

Am sure you have a thermostat stuck open, i suggest replace it and make sure the aantifreeze is in the correct level.

Very correct the ECT is a 2 wire thermistor,when coolant temp increases, the resistance andsignal voltage decrease,If you disconnect the sensor the fan goes on, you just trouble shooted the vehicle cooling fan switch, If anything the signal to the gauge itself may be non-op and not getting to the indicator, try this with vehicle at warm up temperature if you turn the A/C does the fan turn on.it should if it doesnt the power juction box (fuse and relay in engine compartment should be checked, for any opeen fuses, By the way the guage information is from the PCM

u need to take somewhere and have codes scanned (most parts store do this for free) my best guess is it probably a bad coolant temp sensor (u have 2 of them one for gauge and one for computer) one that probably bad is one for computer (should be one with two wires)(one with one wire is for gauge) if temp sensor is reading that the motor hot it will adjust air/fuel ratio for a hot motor but if motor is actually cold it run bad
But to know for sure u need to at least get codes scanned

temperature sender unit top of engine cylinder head make sure its okay
and make sure wire going to it is not grounding
if it grounds or earths it will send the gauge up and down

replace the temp sending unit on the engine first

As long as your gauge is still moving up, there's no real problem. You have heat coming from the heater. It's only a problem if it's getting too hot. What's going on is that you don't let the vehicle run long enough, and it's so cold outside that the engine stays cold. It raises in temp when your stopped because there's no airflow through the radiator. The thermostat just heats up the engine block, and won't change the reading on the gauge. When this goes bad your car will overheat in just a few miles.

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.

My mechanic in our town did a quick computer check. Car computer indicated a low level of antifreeze, he topped it up, cleared all messages off the car computer and said to watch the the heat guage for any further irregularities. I'll keep an eye on it, love the car, great mileage fun to drive.