Join Date: Nov 2007
Feedback Score: 0 reviews
Before you do something rash, get the computer reset for the new tire size, not only is your speedo off, so is your ODOMETER, which will throw off your hand calculated mileage. Also, its winter and as such winter blend diesel is being sold at most stations in the US. Winter blend contiains kero. which has less heat capacity per galon than diesel. Therefore it takes more of it to produce the same amount of work as a gal. of diesel. Also in winter when the truck is cold, the computer employs a cold start strategy that will enrich the mixure for easier starting and warm up, this consumes additional fuel. Further the parasitic losses are higher in cold temps, the tranny, rear/front ends and crankcase oils are thick when cold and take more time to warm up to optimal temps, thus causing increased drag. There may be other things but thes will account for most of your mpg dropoff.
I've driven diesels for better than 20 years and during the winter all of them experienced lower mileage, but returned in the summer.
BTW the tire size increase will have an effect on your overall rear gearing, however slight, that will cause you to use slightly more fuel to accelerate from a dead stop.
2012 F550XL 19,500gvw, Oxford White/Steel interior, 6.7psd, Stainless simuators, Sync, 16Ft Morgan body, Waltco tuckaway 2500 lift gate.
2011 F250 CC Lariat Ultimate, Royal Red/Pale Adobe, 18" wheels, 3.31 locker, 172"WB factory Nav/Sync,etc.
Also have a 1997 F450 7.3 XLT with 14' box, Hypertech programmer
1987 F350 6.9 Banks Sidewinder, 12' box
Still going at 200K+
Traded:08 F250 CC 4x4 Lariat, 172"WB
Traded:01 F350 CC 4x4 Lariat, 172"WB