Had an interesting thing happen yesterday, first time I’ve seen it.
In the morning, I checked my coolant level and it was a little low (normal for my car - I usually lose about a half quart of coolant every couple thousand miles), so I topped it off with distilled water.
All was good, then in the evening, on the freeway, I looked down and noticed my temp needle was almost all the way to the top. Probably 7/8ths of the way to red. I freaked out and immediately got off the freeway so I could stop, but then I noticed the temp was slowly dropping back down to normal, so I got back on the freeway. Then the needle starts climbing and almost hits max temp again, so I pull over and stop before I damage the engine block or something.
Pop the hood, and everything looks normal. Engine doesn’t feel hotter than normal. Coolant level still fine. No steam or anything anywhere. Never got any dashboard warning lights or anything. Scratching my head, I start the engine again, and the needle immediately is showing normal temperature again. Since the engine was only off for about 2 minutes, there’s no way the temp actually dropped that much. Figuring it must be a sensor or gauge issue, I decided to go ahead and drive home, and haven’t experienced the same thing again yet since then.
I’ll go ahead and rule out the temperature itself being an issue, since there was zero indication of overheating symptoms. What kind of other issue could cause my temp needle to climb for no reason?