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Old 01-07-2016, 05:45 PM   #1
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Default Want to talk Series 60 fuel economy?

My instant read averages 5.5mpg sometimes creeping up to 7. I haven't done any actual calculations yet.

Anyone else with 515hp Series 60 Detroit care to share some fuel economy figures? It seems acceptable on the trucking forums, but I'm only hauling about 35,000 lbs. (sometimes 42,000)

The truck has been gone through by two Freightliner dealerships in the last few months and they haven't noted any issues. I'm not complaining about the economy, I just want to know if it is in line with what others have experienced.
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Old 01-08-2016, 12:00 PM   #2
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First off don't believe the computer, I have hand calculated and compared it to the display and have found major inconsistency between them.

My coach gets between 6.5 and 8.5mpg (hand calculated) depending on travel speed, terrain (hills vs flat), wind, cruise control use, generator on or off (affects fuel mileage as it uses fuel from the main tanks), towing car trailer or not, how much stop and go driving. Tire pressures and even trad design can also contribute.

I find speed to be the single biggest controllable factor that affects mileage. I can get better fuel mileage running 60mph pulling the trailer with my Dodge 1ton diesel 4x4 on it than I do running 75mph with just the coach.
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Old 01-08-2016, 01:00 PM   #3
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I agree with Porky. I usually tow a Suburban and drive 1-2MPH over the speed limit on the interstate using the cruise. I also always travel with a full H20 tank. 7 to 8 MPG.
I have tandem axle's and have the Eaton 10 speed auto tranny. Head winds seem to make the biggest difference in MPG. I can drive over the Rocky Mts and still get the same average.
If I slow down to 58 MPH, like on a state route road, I'll get around 9 MPG. We are pushing a big square box down the road, not the greatest aerodynamics!

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Old 01-08-2016, 03:10 PM   #4
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Thanks for the input gentlemen. I will start doing some real mileage computations and see where that leaves me.
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Old 01-10-2016, 04:23 PM   #5
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I don't have a Detroit, but my Cummins ISX15 gets 7 mpg running at 70-72 mph as calculated by several tanks filling and mileage calculated by hand. I don't really notice much mpg difference if towing trailer or toad vs MH alone. I am about the same weight and size as you are.

I could probably get better mpg if I would go slower, but time is of the importance to me. I want to get to the location. Plus in general I hate being stuck in slow lane.
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Old 01-11-2016, 08:35 AM   #6
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I too prefer to keep up with traffic. However, I fear that the truck's optimum cruising speed is 65mph. The highways around here have a 70mph speed limit, and most traffic moves at 75 (semi-trucks included). I prefer to plug along at 70-73, unless I am contributing to a slow down, then I will pick up the pace until I can find some clear road again and no one needs to get around me.

I began this research because I had read on some of the trucking forums that the Series 60 programming may be able to be altered to shift the engine's optimum cruising speed a bit, while retaining or even improving fuel economy.

As soon as duck season is over, I plan to head South for a few days. Along the way, I hope to take a closer look at the fuel economy and establish some mpg numbers at various cruising speeds.
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Old 01-11-2016, 12:38 PM   #7
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from the FWIW department:

We're equipped with the MBE4000 (DD13 equiv.) factory tuned to 450hp with a 12speed Meritor SmartShift Tranny.

Moderately loaded were 36k lbs (130g / 210g of Fuel/Water). Ive seen as high as 13mpg (mixed driving from blacksburg va to destin fla) and as low as mid 8mpg. On average (houston tx to the northern shenandoah valley) we see mid to high 9s if we hold it to 65mph or less.

More often (keeping up w/ traffic) we see high 8s to low 9s (72mph cruise w/ the occasional burst to get around traffic).
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Old 01-11-2016, 11:01 PM   #8
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Just remember that Don's figures are for a single drive unit not a tandem drive and that will naturally give you slightly better mileage as there is 4 less tires rolling resistance and one less differential being powered. But they are a good representation that a chassis speced differently doing the "same" task can get fairly different results.

I personally think they gear these units too fast (numerically low) being as most are in the 3.08 range. I think 3.55 would work better.

I owned a 2000 Peterbilt 379 long hood, big sleeper, true 600hp Cat (not the best reputation for great fuel economy) 18sp, 3.73 gears, 24.5 lo pro tires, 46k rears...fairly heavy specs for a highway truck, pulled a triaxle(102,500lb gross) in Canada and a quad axle(96500lb gross) in the NW states and when driven rationally I could average 8mpg, and as high as 12mpg when running empty.
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Old 01-11-2016, 11:37 PM   #9
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good point!
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Old 01-12-2016, 06:59 AM   #10
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So reading between the lines here. If I put my right foot on a diet and my manual calculations still yield 5.5mpg I may have a mechanical issue? Over on the trucker's forums they talk about air leaks causing economy problems, I guess it would bark up that tree at that point. Thanks for the insights.
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