Do I need a new thermostat?
 

Up till this week, my temp gauge rarely went to half way... (keep in mind, up until this week, the temperature really hasn't spent much time above 50 degrees outside.)

During this week, on the drive home from work (55-65 degrees) I noticed my temp gauge would rise to about half, maybe a tad above. Last night driving home from the store, it got this high... I'm mildly concerned, but have no Idea what steps to take to remedy the situation...

It doesn't leak coolant, the radiator is still full, the overflow tank is just above half full... Could my thermostat be to blame? I'm not really running the engine very hard (1 run up to 7K in first and second gear on my drive home.)

Bump of justice... I'd prefer to fix this before monday

thermostat is $11 so just change it

If it's not the thermostat, what are some other things I should look at?

If the car gets hot but the upper radiator hose remains cool, then coolant is not circulating. 4 reasons why that can happen:

Waterpump failing
Thermostat stuck closed
Large amount of air in the system
Clog in the system from rust and debris

Changed my thermostat today, bled the air out of the system, and didn't have too much time to drive, but after 5-10 minutes of light driving it was still hovering around the half way mark... Isn't it supposed to stay closer to the 1/4 mark?

yeah... ive had problems with the belt slipping recently, if you have no air pump this is worth checking. the other overheating cause ive had is the radiator, but i'm usually buying cars with plugged radiators, so i don't think they can all of a sudden clog?

I drained quite a bit of coolant out before changing my thermostat, it took near as makes no difference a gallon to top back off. There were a couple rust flakes, but considering how well it flowed out and how clean it otherwise looked, I'm doubtful it's clogged at all. I did tighten my alt/water pump belt a tad too, after noticing how loose it seemed. I may have to loosen it a tad though, because it squeaks under higher loads.