Temperature Gauge Rises and Falls

[Zepod]

I was driving down the road today and I noticed that my temperature gauge kept rising to hot when I came to a stop and then dropped back to normal when the automobile was in motion. At times, however, it did slide just a little below normal to cool.

I have no idea where to start, could it be a leakage?
Needing of more coolant or water in the radiator?
Replacement of the water pump?
or
Replacement of the thermostat?

Any help would be appreciated.

I drive a 2009 Mitsubishi Galant.

 

[Alan11]

this is usually because there is air in the cooling system.. bleed the system!

are the fans working properly?
are there any leaks?