It cant be the sender because we are comparing the temp before a coolant and thermostat change and after the change. The sender is a non issue. The temp before was 85 and after was higher. Even if the sender/gauge is inaccurate at 85; the temperature was higher after the service.
I took the car for a spin to double check what I am seeing on the gauge. There is a mark at 80 and one at 100 on the gauge so I assume that exactly halfway between is 90 degrees and 3/4 the way is 95 degrees. Looking at it closely; it seems to be probably about 92-93 on the gauge so thats a little better than my initial readings.
I'm nitpicking here and dont mean to imply that anything is wrong with the cooling system. It just seems that the new thermostat is probably beginning to open at a temperature higher than the indicated 80 degrees and is fully opening around 92-93. The old thermostat was fully open at 85 degrees.
Again, no biggy.....just wondering if this is common with a new Behr thermostat and if the Wahler's are more accurately calibrated; therefore better than the Behr's?
I guess the only way to find out is change to a Wahler and see the results.

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1985 300TDT
2013 E350 Bluetec