New truck on factory oil......ran it abut 2k. I then ran Rotella for the next 20k, dropping it every 4k. I've had the truck on a steady diet of Delvac-1, changed every 7k or 300 hours, which ever comes first. Well, I just checked my fuel mileage after a little jount down the road of 250 miles. My avg speed was 37 MPH and my MPG has gone up by 1.1 MPG! :ro) ........ I'm in the South and I do not believe the truck has had a tank of winterblend this year. Could it be that the Delvac-1 prolongs engine life that much? I noticed I had gotten a little better on my last tank or two..but I did not check it until now.

Did you expect your engine to start wearing out after 50k?
Your low speed helps mileage a ton as I've seen on a couple of occasions.Late last year I got a little over 19 mpg in and out of 4 wheel drive but driving on average 40 to 45 mph.The slow speed makes a huge difference.

I managed 20 mpg flat on my maiden voyage (<2000 miles on the odo) from denver to CA. Went about 75-80 the whole way home.......

I have a hard time believing all of this "break in mileage" stuff.

Burner - Do you have good records for your mileage from the beginning?

NWDmax, The truck was driven over 70MPH *except* for the Idel time (about an hour total) and the little bit a racing down the hwy.

Manny, records of 99% of every tank full.

What was your average at 10k, 20k, 30k, 40k, and 50k?

Any difference in your driving habits?

Improved @ 30k then @ 40k and now @ 50k. I drive the same way all the time....... It's a two speed.......STOP and WFO.:ro)

Burner,darn good mileage I hope mine continues to improve with age too!
Most of my trips running 70 to 75 mph I get between 17.5 and 19 mpg.
I figure the wind is the biggest variable and accounts for the differences from trip to trip on the same route.

......... in all honesty my Mileage has been 11.7.........then 12.1.......roughly 14 .......and now 15.1 on the Hwy. Yes, I have always had really crappy fuelmileage. Had two trucks.....one *totally OEM/stock* and one pumped up.....they got the same MPG. I don't know why?....... I guess i'm just lucky that way? :rolleyes: