Chevy Duramax actual mileage results

[dznf0g]

Originally Posted by fltlevel510

I have a 2005 silverado 3500 with the Duramax and Allison 6 speed transmission and have been getting over 50 mpg while towing. As others have said the secret is RPM. By adding the Eaton 2 speed differential and using a blend of jet fuel, water and acetone it is not uncommon to get these superior results. Additionally, water vapor creates absolutely beautiful contrails behind the airstream. My next mod is to add a duel exhaust system in an attempt to create a dual contrail. My only problem has been towing at speeds over 100mph I get an overtemp warning from my tire pressure monitoring system and stopping distances have increased substantially.

Disclaimer: All data was collected with a vehicle equipped new tires, new brakes, a recent wax job and production test pilot at the controls. Your actual results may vary

LOOK OUT!!!! there's a bunch of trees in front of you! PULL UP!!!!! PULL UP!

[flyingfinn]

It has been very educational for me to read the various hints about mileage that various AS owners have given since I started the thread. Thanks. I pull a 2008 28 footer with my 2008 Silverado 2500 HD 4x4 diesel. I reported that I get 12.4 mpg. I do not have a cover on the bed nor a cap. Would those increase the mileage?

[Sky]

I don't think so.

[dznf0g]

Originally Posted by flyingfinn

It has been very educational for me to read the various hints about mileage that various AS owners have given since I started the thread. Thanks. I pull a 2008 28 footer with my 2008 Silverado 2500 HD 4x4 diesel. I reported that I get 12.4 mpg. I do not have a cover on the bed nor a cap. Would those increase the mileage?

Not by much at all. Trucks are designed to create a bubble of air which sort of "stagnates" and rolls slowly in the bed area. If you drew an imaginary curve from the roof to the top of the tailgate, that is the shape of the bubble. That's why you'll find very small shape features on many trucks, like the bed a bit narrower at the tail than the front, little "spoiler lips on some, etc. A Topper creates a flat suction surface at the back. A Toneau cover probably neither helps nor hurts. Some believe that a fifth wheel ventilated gate actually hurts.

All these things affect mileage so little that you probably couldn't significantly measure it with bigger variables in play, and certainly would not be the sole reason to purchase.

[SteveH]

I have a camper cover on my GMC, and it certainly does not help mileage. My "gut feeling" is while towing it doesn't hurt mileage, but while driving solo, I think it does hurt the mileage slightly. This I have reasoned by comparing what others report, however others report they drive 60-65 MPH. I typically drive faster. I know if I drive under about 62, my truck does not go into 6th gear while in the tow/haul mode.

[dznf0g]

Originally Posted by SteveH

I have a camper cover on my GMC, and it certainly does not help mileage. My "gut feeling" is while towing it doesn't hurt mileage, but while driving solo, I think it does hurt the mileage slightly. This I have reasoned by comparing what others report, however others report they drive 60-65 MPH. I typically drive faster. I know if I drive under about 62, my truck does not go into 6th gear while in the tow/haul mode.

I would agree with this analysis.

[slowmover]

A topper only "works" when it follows the lines of the truck very closely. In which case the single "flat wall" at the far rear of the truck trumps the aero problem of two shorter "walls" (cab to bed & bed to tailgate). But a hard bed cover seems better overall, especially as crosswind sail area is reduced in comparison.

An "aero" bed topper is best of all (along a 12-degree drop from cab roof to tailgate).

[Streamside]

Thought I would post this trip we just came back from. Not great but not bad either.
2002 GMC Duramax (now has 206021 miles) CC, SB, Lear camper, EU3000IS
2001 70th Anniversary Slide-out 30Ft(actually 31 but who's counting)
ProPride Hitch, Sendel wheels w/ 235 75 16's Michelin E rated @75psi
trailer loaded and with a full tank of fresh water---
Steering axle-3910lbs(98% restored), Drive axle 4110lbs, Trailer axles 8160lbs (8 tons rolling, Trailer with hitch at 9140lbs---40 lbs over)

Starting Altitude---4600ft, max altitude on trip (Eisenhower/Johnson tunnel @11,158 ft, ending altitude at lake michigan 581ft

Mostly driven at around 65 but topped the continental divide tunnels AT THE SPEED LIMIT---maybe just a little over just because I could.

Miles driven 2664.6 (odometer)
Fuel consumed 209.33 gallons(US) (Receipts)
MPG 12.73

BTW... If anyone finds my "stinky slinky" on the side of the road between Denver and North Platte.......