Air pocket in the system maybe? My thought is that when the gauge does that, the air pocket has shifted to where the sensor is and is causing the sensor to "heat up" because it's not being cooled by the coolant. Might think about burping the system and seeing if you get any air out.

Richard <img src="/forums/images/graemlins/patriot.gif" alt="" />

Had an 89 Isuzu Pickup
Had a 94 Mitsubishi Eclipse
84 Honda XL185S
Had an 89 Isuzu Trooper w/ 3.4 V6
01 Toyota Tundra SR5 V8 4Door Access Cab
http://community.webshots.com/user/rsayloriii