I bought a 2003 Galant about a month ago from a neighbor. car is in fantastic shape after I replaced the timing belts, spark plugs, and windshield (now if I can figure out the A/C...). The only issue I noticed after driving for a while was the temp gauge goes straight to the mid-point after driving for just a few minutes. Could this mean the gauge itself is bad, also, I have been told could be thermostat issues?

Thanks.