I have read two other threads that indicate a leaky head gasket for Nissan Frontiers overheating...but I'd like an opinion on my problem: I have a 1999, v6 3.3L, 4x4, manual Frontier that I have owned since 2001, always well-maintained, timing belt, water pump and thermostat already replaced a couple of years ago; currently has 129k mi. I rarely drive it (about once or twice a month). Last time I drove it (I'm in AZ and heat was over 100 degrees) it started right up and was fine until I'd gone about 3 miles on the freeway doing about 65mph. Started to climb in temperature, but not into the red zone. I drove with it hovering just above the midway point (midway meaning perfectly normal temperature on my gauge) for a couple of more miles, when it started to climb just a bit more, I got off the freeway and dropped under 45 mph, the temperature went down to normal. I drove about 40mph back home and haven't driven it since. I checked my coolant, which was extremely clean and not low, and was not boiling when I checked it soon after the temp went up on the freeway. What is the most likely cause?
On a side note, since I do not drive it that often, what is recommended as to the gas that has been sitting in my tank since? How long does the gas stay good for? Further wondering how often it is recommened I drive it, for how long and at what sustained speed to keep my truck up and running?