Do not drive the car till you are sure the *radiator is filled to the top when the engine is stone cold. The plastic coolant recovery bottle should be 3/4 filled also. Unless engine coolant flows around the *temperature sensor in the cylinder head, the dash gauge will resister nothing. Of the radiator is full and you're getting no heat on the dash gauge, the electrical temperature sensor needs to be replaced. Ask the dealer of the car IF the thermostat is working normally. If you're getting plenty of heat out of the heater, the thermostat is OK BUT the temperature sensor in the cylinder head is NOT OK.

There are 2 possibilities here.

One is that the guage or sender is faulty and just isn't registering the temperature. This wont cause a problem itself, but you wont know if there IS a problem, like a leaking radiator that causes the engiine to overheat. You wont know until the engine siezes.

Second possibilty is that the thermostat is stuck open, and the engine is actually running cold all the time. This isn't immediately fatal, but it will affect the fuel economy and cause faster engine wear.

So you want to work out what is wrong and get it fixed. Guage, sensor or thermostat. The car is probably safe to drive in the mean time, but it is an issue.

If the guage in the dash is faulty and expensive to replace you may be able to get an aftermarket guage and just mount it on the dash.

Your car won't overheat just because the gauge has ceased operating. Many cars did not used to even have a water temperature gauge.

It is however pretty important to be able to monitor the engines temperature from a 'peace of mind' point of view so get it fixed at the first convenient opportunity.

Before going down the "it could be" path, what do you mean it doesn't move? When you get in the car, before you stick the key in the ignition, what does the gauge register? When you then turn the key to "run", does the gauge move at all? And then once running I am assuming it doesn't move at all as the engine (assumedly) warms up?

It can, and if it does your first warning could be steam out the front of the car grille. If it does overheat, also consider that many cars are using plastic tanks on the radiators, so those can crack.

The car will operate normally regardless of the functionality of the temperature gauge. I would replace the dash cluster or check for unplugged wiring connectors or faulty wiring

It shouldn't, if it just stays at the lowest temp (as if the ignition isn't on) probably just a thermo issue, or a sensor. check your coolant, ride it around the block a few times to make sure it doesn't overheat. and if no problems. just check your coolant every time you drive, get it fixed asap.

then replace the temp sensor. "muffin"