When we started this summers trip, the engine was basically new. Only enough miles to get it from Elkhart to Ft. Meyers to Palm Beach. Also the ScanGauge needs an engine specific "calibration" to measure gas consumption. Never having done this before for a gas engine, I also had to figure it out from scratch.
Early on the calibration started around 9 %. Tank by tank I immediately found the the average mpg zeroing in on 9.4. However, the engines behavior steadily changed as indicated by the calibration value slowly getting lower. By mid June (4300 miles) the engine stabilized at a calibration of 1.3% as we toured in the cooler climes Door County, WI and around Lake Michigan.
Once back into the hot weather (5500 miles) the engine changed slightly as the calibration climbed back up to around 2 %. By the time we reached 9000 miles the calibration stabilized around 3%.
All this time there was no indication of anything changing because the average mpg never changed from 9.4. Total miles now is around 10,000. Hopefully the E-450 is now broken in and stable.