Cooling Problems and Possible Upgrades?

[RoadWarrior]

To check if the head gasket is blown you should be able to just take off the rad cap (while the car is cool) and watch for bubbles. If its really bubbling you have a blown head gasket. But my best guess would be the thermostat or the sender. Both are fairly cheap and easy. Head gaskets dont usually blow unless your either running higher compression, the engine gets too hot, or it wasnt installed properly. But im betting its the thermostat. Hope its just something small.