New 3-way coolant control valve improves MPG?

Recently I replaced the 3-way control valve in our car. It was half way through a tank of gas - eventually burned through that and then filled up. Oddly since that fill up the car is doing exceptionally well MPG-wise, the calculated fuel efficiency for 160 miles is 49.3, which is 2 or 3 MPG better than it usually does. Same sort of driving. The valve only just recently threw a code, but maybe it wasn't working quite right for a while before that, so that the car is finally showing the added efficiencies that the thermos is supposed to provide? We do make quite a few short trips, so the faster warm up of the motor could actually be making a difference.

The only other variable was that it was filled at an ARCO, instead of the Valero, Sam's Club, or 76 we usually visit. Never had a tank of gas make things better before, so it doesn't seem likely that was the issue.

Or this could just be a random statistical swing in the fuel efficiency.