If we look at what can cause the temp to fluctuate in this manner there is really only 3 options,
. Your new thermostat is faulty (not the first one to be)
2. The internal core is partially blocked (but this would normally cause a more constant occurrence)
3, Air pocket in engine, (same as above)
Fan switch is coming on when temp is high? Not a problem with a switch that is a bit temperamental?
I would discount a water pup problem at this stage, and one last question, is the coolant level constant, no evidence of loosing any coolant prior to an event?
Thursday, December 13th, 2007 AT 3:58 PM