As Spike once said, "Buy an Ultragauge. Then you'll have a whole bunch of new things to worry about."
My water temp went up two degrees, from 198 to 200, immediately and exactly after I discovered the negative terminal clamp was loose on the battery. I was just poking around, doing general inspection and maintenance, and had not experienced any difficulty or symptoms, when I found it. The previous owner had replaced the factory cable, which has always been still in the truck un-connected. I noted it has a tie to a ground "bus-bar", so while I was tightening the terminal clamp, I hillbilly engineered a way to use both cables, and connect the factory cable to the negative post as well.
As I said, temps up two degrees first trip after repair. I'm wondering if this is simply a sensor issue, with a new, improved "reference" or earth ground. Anyone else ever exprienced a similiar situation?

 

Mutually exclusive. Can't see how the two would be related.
Coincidence?.

 

You changed the ground reference point, and the ECU recalculated the sensor input. I've noticed on my D1 that temps usually jump by 2-3 degrees as opposed to 1 by 1, I put this off to the design of the analog to digital converter inside the ECU.

Removing the sensor and cleaning the calcium off of it may change reading. Skinned wire in harness or gunk in connector may be providing another path to ground.