At 120,000 miles on the Delvac 1 oil of my 2006 Volvo 780 (w/ Volvo D12 engine) and about 650,000 total miles on the engine, oil analysis suggested I finally change the oil, so I did. I discovered my MPG on flat land w/ MT trailer dropped from around 9.0 MPG to around 8.0 MPG!!!

The good news, is that after a few thousand miles, my MPG is back up to where it should be. :smokin::smokin::smokin:

mine did the same.. i'm wondering if its the winter blend fuel?

I buy all my fuel in FL, so we don't have winter blend.

Have you had oil sample done? All I can think of is the fresh oil was thicker, as maybe the old stuff lost viscosity possibly due to fuel oil dilution. Hope not for your wallet's sake.

The oil analysis said there was no fuel, water or glycol in the oil.

I can't think of nay reason why that would happen. I've never noticed it happen to me with 20,000 - 30,000 intervals and dino oil.

I'm still trying to digest the fact that a truck driver can spell
[h=2]Significantly[/h]

Spell Check is a wonderful tool.

I'm thinking with YerDaddy, sounds like a heavier weight oil went back in than what was spec'ed. I know my personal vehicle got crappy mileage when I ran 10W until it got about 4,000 miles in on normal everyday driving to and from work. After that the mileage jumped up about 3 mpg. Of course on long distance trips 10W actually got better mileage than the 5W got.

I am an engineer by degree. I launched rockets (Atlas, Titan) at Cape Canaveral Air Force Station until 05/05, when I became an O/O.

I tend to believe, oil has nothing to do with it. Or at least didn't played a major role. In any case it takes more than a small viscosity difference to loose a whole 1mpg! Probably combination of factors, but since it's back to normal, i wouldn't pay much attention to it....