It's a common known fact that the stock gauge is useless for accurately monitoring the coolant temp. The stock gauge pretty much stays still at "normal" temp from ~170 degrees to ~220 degrees.

If you're seen the gauge fluctuate it is because you're either dancing around just below 180 or above 220, and if you're above 220, you're already in trouble.

The large temperature change I saw was not seen in the stock gauge, how do I know? I looked at both. The fact that the senders for each gauge are 1.25" from each other, you would think they're reading the same temp, regardless if they're on opposite sides of the t-stat.



On a wildly more relavent note...
Iit's warmer out now. The gauge isn't doing it anymore, which leads me to believe my theory is right.