Something I've noticed with my overhead. I drive about 27 miles to and from work each day on the freeway. The meter often starts to climb quickly during the last 10 or so of those miles each way. This morning it was at 18mpg the whole way, then climbed to almost 19mpg during those last 10 miles. Typically, the last 10 miles on my way to work is the fastest part of the drive. People speed up here to 75-80 and it still climbs where the rest of the drive is more like 70. Has anyone else noticed this? I've heard these motors take a while to really warm up so I'm wondering if perhaps those getting low mileage are commuting shorter distances and their trucks just aren't opperating at peak efficiency yet.

 

Temperature has a LOT to do with engine efficiency. Engine temp is affected by many factors including ambient temp, load on the engine, time spent running, etc. You will definitely get better MPG while the engine is warmed up on a warm day. Conversely, the worst possible condition would probably be ~1 mile trips all day in subfreezing weather... the engine would never get a chance to warm up at all.