97 Ranger 4.0 temperature guage

My 97 Ranger after about 10 minutes of driving the temp guage pegs the hot side, then after about 15 seconds goes back to normal in the middle range. Then it will do it again and go back the same way, about 15 seconds on pegged. Could the sensor be bad? I havent done any long driving, I am at work in about 10 minute drives. I havent put any coolent in it for over 3 years, coud it be as simple as that?

Are there any heat related issues besides the temp gage? Do you ever check coolant level? Does the radiator fan run? Check the thermostat?

If you have a radiator cap and coolant recovery bottle, if it gets too hot, it will pop the cap and the coolant recovery bottle will fill up in a hurry.