Fuel Mileage

Broompilot · Feb 15, 2005

I am very light footed, I am the truck that is always getting passed, easy on the up hills unless loosing mph average 3-4 under the speed limit unless Ohio or IL. Truck is acting like an 18 wheeler when it comes to fuel mileage. 7.2 to 8.5 Cummins 285hp Allison 5spd rear end I believe is 380something. I knew I would not get 10 11 with the Auto but in the 7's is just a little to low. I use a diesel non gelling agent would the Cetane Booster help?

Glen Rice · Feb 15, 2005

While the truck is under warranty, you may want to take your unit to a Cummins dealer and tell them your mileage story. They may reburn your computer with the latest greatest updates. Winter time and idleing are the biggest fuel burners going. Not to mention the winter blend fuel has always big soft on mileage. Good luck.

LDB · Feb 15, 2005

I'm seeing similar problems. I picked up my truck on 9/24/04 and for the first 10k miles got about 9.46 mpg. The second 10k miles it was about 9.29 mpg. I didn't think that was bad since the first 3500 miles were empty going to orientation and back to Texas to get base plates etc. and the second 10k miles was all working. The third 10k miles has only produced 8.32 mpg. My driving style hasn't changed and my loads haven't changed. The only difference I can think of is the winter fuel. I'm hoping it will go back up. I've had it in the shop and got no improvement but am planning to put it in once more since it's under warranty. I'm also planning on a different powertrain on the next truck.

Leo
truck 4958

Support the entire Constitution, not just the parts you like.

gojack · Feb 15, 2005

LDB
you do not say how your current truck is spec'ed
also curious what you plan for next time?

Dave

>I'm seeing similar problems. ... I'm also planning on a
>different powertrain on the next truck.

davekc · Feb 15, 2005

The two major items I am seeing is you have to use winter blended fuel and a 5 speed tranny are going to bring those numbers down. In the summer you should be around 8.
Davekc
owner
20 years

silverdollar · Feb 16, 2005

Read your owners manual, it will tell you at what mileage you need to run an overhead,(valves adjusted) after I had mine my miles jumped about 2mpg.

LDB · Feb 16, 2005

I don't have a build sheet on the truck. It is a Sterling Acterra 960 from Freightliner of Knoxville. It has the MBE 926 engine at 300hp/860tq. The trans is a 6sp auto. I believe the rear is 4.58 but don't know for certain. At 65 it turns about 1700 rpm.

My next truck will either be a Sprinter van to simplify things or it will be a class 8 with a big block engine tuned to around 400-430hp. It will have a 10sp auto to lessen the rpm gap between gears. It would have a lift axle and 44-46k gvw to carry super D class loads.

Leo
truck 4958

Support the entire Constitution, not just the parts you like.

Tom Robertson · Feb 16, 2005

LDB...

I am not sure why these on the lot trucks are spec'd with the rear end ratios that high. Maybe most striaght trucks are used in town... but as an expediter you'll be much better off with a lower ratio.

I have M2 with the MB 900 engine with a lower HP than yours (260).
I spec'd them with .357 rear ends and get 10-11 mpgs.

If I remember correctly you have a new truck. It would be in your best interest to have your truck changed out to something similar to the .357 The savings in fuel alone would pay for the conversion pretty quickly... then the remaing time on your truck would be spent more profitably.

LDB · Feb 16, 2005

I emailed Sterling and turns out my truck has a 4.78 rear. I could lower it somewhat but don't know how far I could go without putting it so low it would never shift up to 6th gear. As it is I have to get up to 60mph to get into 6th and it will downshift when on cruise control just to cross overpasses. I'm going to contact Detroit Diesel and see if they can tell me the optimum cruising rpm for this engine. I might look into a gearing change so it will cruise at that rpm if it's enough of a change to be worthwhile.

Leo
truck 4958

Support the entire Constitution, not just the parts you like.

davekc · Feb 17, 2005

LDB
Prior to making a change, you need to know what the gear ratios & torque requirements are in your auto transmission. They will be different than Tom's set up because he is running manual transmissions. Most dealers will have a program that they can access to provide you with the correct info.
Auto transmissions are expensive to repair so you need expert advise prior to any changes with the rear end. This could turn into a nasty situation if not done correctly.
Davekc
owner
20 years

LDB · Feb 17, 2005

Yeah, I'm afraid it's probably just going to have to stay as is. I doubt I could change it enough to make it pay off. If I did change it I'd never get to 6th gear unless I was in a 65mph or better state. As it is I have to get to about 61 for it to go to 6th and then maintain at least 59 for it to stay in 6th. I may still contact DD to see what they tell me but doubt I'll modify things any unless it's going to make a major change.

Leo
truck 4958

Support the entire Constitution, not just the parts you like.

davekc · Feb 17, 2005

Yeah, I'm afraid it's probably just going to have to stay as is. I doubt I could change it enough to make it pay off. If I did change it I'd never get to 6th gear unless I was in a 65mph or better state. As it is I have to get to about 61 for it to go to 6th and then maintain at least 59 for it to stay in 6th. I may still contact DD to see what they tell me but doubt I'll modify things any unless it's going to make a major change.

LDB
Along with what I had listed you are correct in that you would have a late shift from 5th to 6th. However, that can be changed on the engine computer. As long as your engine is computer operated this can be done. Parameters for engine speed, idle, shift timing ect. can all be done by the dealer. They do have to stay within certain guidelines or it will void your engine warranty.
Davekc

Broompilot · Feb 19, 2005

Just came off short week, bitter cold New England. Mileage improved to 8.4 go figure. Even got a ticket (warning) for 60 in 65. Cop really wanted to check registration as IRP plates do not have year sticker on them, and also he wanted to see my camera system not kidding even called two other troopers to see it I had three police cars behind me before this was over. I let them in and showed them everything they were quite impressed.

Went the Cummins dealer this morning going to call a man there who is suppost to be able to figure all of this for me. I have a gut feeling that 9.5 in the summer is as good as its gona get. As for why (Toms question) The rears are that high to keep the torque on the engines low it was explained to me or you have to go up to the 330hp 7 or 10 spd in these trucks with this type of set up. Talked with a C&M driver same truck as mine with his being a 7 spd. Mileage was only about a half more than mine. The price you pay for comfort, I will stay pay it after all of the bull ^#$%& thru NY Balt, and D.C.

KW gets a great deal from Allison and Cummins to order this many trucks and keep the price down so take it or leave it. Glad I took it the more I drive the happier I am with this truck esp. after looking at all of the M-2 complaints on this site. (so many I wont even bother reading them).

Larry I am running the same RPMs as you 70mph 19 65 15 60 13

Marmino · Feb 19, 2005

I doubt you remember us but we were admiring your truck at the Troy Freightliner dealership when you apologized to us when we told you we had a Freightliner by Alumi Bunk. Apology accepted, we get 9-10.22 mph depending on the load.