This is driving me crazy. After sitting outside one really cold night, my truck coolant guage started really acting strange. It moves around over a 20 degree temp range back and forth slowly while I drive. Doesn't seem to correlate to any driving type...like it isn't everytime I stop it rises or anything, it just seems to happen steadily whether I'm in stop and go traffic or whether I'm crusing at a constant speed. It just slowly climbs..just to the point to make me scared, the slowly goes back down and repeats very slowly. The engine is freshly rebuilt with 2000 miles on the rebuild. Cooling system is entirely new at the time of rebuild including gauge sending unit. I swapped the thermostat and it had no effect. Anybody every experienced anything like this?