A few weeks ago, I was on a short drive and noticed the loud rushing sound of the aux fan kicking on. I looked down and the temp gauge was just under the red. After only a few seconds, the temp dropped rapidly to normal and then sat there rock solid for the rest of the time I was driving. The repeated about 2 weeks later and then a third time about another week after that. Each time it happened, it was as the engine was warming up from cold. Each time the aux fan was audible. Each time, the temp was only high for a few seconds before returning rapidly to normal. Coolant levels appear to be OK, and I have no major leaks (1 very minor one, but it only leaves a few drops after being parked overnight) Does this sound like a sticking thermostat? Or, is there something else I should be looking into?