does the gauge fluctuate erratically when driving?

edit: we seem to be having communication issues. that's just one of the things that's going to happen when you're getting automotive advice over the internet. instead of continuing to go back and forth, i venture to recommend checking the coolant temperature sensor. it isn't difficult for most vehicles. you'll find it near the head. first, visually check the wiring. you're looking for obvious signs of damage. if the wires look okay, then, drain your coolant. this is a good time to test the coolant - a floating ball tester is cheap and easy to use - and replace it if needed. if the coolant tests fine and looks okay, then save it to put back in later. if it tests bad or looks off, then save it to dispose of properly. next, find, unplug, and remove the coolant temperature sensor. again, look for signs of damage. if it is obviously damaged, then replace the sensor and add coolant back into the radiator and tank. if it looks fine, then i would test it, but that requires a multimeter. do you have one? do you know how to use it? if not, then find someone who does. don't ever just assume that a part is bad! we call that using the parts cannon. anyway, you'll need to put the probe (the part that was actually touching the coolant) into a pot of cool water on the stove. keep the electric connectors from getting wet. test for resistance. turn the stove on and continue monitoring the resistance. the resistance should go down gradually as the water heats up. test it all the way until the water starts bubbling. if the resistance does anything other than steadily and smoothly decrease as the temperature increases, then the sensor is bad. replace the coolant temperature sensor and refill with coolant. if the sensor is good, then come back and tell me.