Yesterday afternoon I noticed that my temperature gauge was all the way in the red. Then suddenly the temperate gauge needle went back down to normal. It would stay in the middle for a few minutes and then rise to hot again and stay there for a couple of seconds and then suddenly go back to normal. There were no other signs of over-heating (no steam, smoke and no burning smell and no changes in the way the car was driving). My husband put coolant in my engine last night but then temperature gauge is still acting up this morning. Any idea what would cause this?