Good Sam Club Open Roads Forum: Towing: MPH vs MPG
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Mike in DE

Delaware

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Posted: 12/30/22 06:08am Link  |  Quote  |  Print  |  Notify Moderator

I bought a 2022 Chevy 3500 6.6L Duramax Turbo Diesel and wanted to check the fuel economy for both towing and not towing. The numbers you'll see DO NOT include regen periods where the engine is burning excess diesel to convert soot in the DPF to ash. Also, the figures are from the truck's DIC (Digital Information Center) screen where the truck calculates the MPG via the trip gauge. Some people say those numbers aren't realistic and tend to be higher than actual. However, I checked those figures with eight stops at the pump (1400 miles in total), manually calculated the MPG and found there was good agreement between the two (within 1% on average). These were NOT fill-ups, rather, they were partials and averaged 14.5 gallons per refill.

You'll see in the table the term "equation". This is the MPG using the trendline fit on the plots I generated. It's an arbitrary curve fit but does match the data pretty well. I'm simply comparing the curve fit with the averages for the speed increments I ran.

I am pulling a 2018 Highland Ridge 5th wheel that is 32 feet long and weighs about 9000lbs loaded.

Hope this is useful to some folks!

https://ibb.co/BCWxTkp

* This post was edited 01/02/23 03:34am by Mike in DE *

deltabravo

Spokane, WA

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Posted: 12/30/22 06:44am Link  |  Quote  |  Print  |  Notify Moderator

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Were these tests done over the same route? In the same direction?


2009 Silverado 3500HD Dually, D/A, CCLB 4x4 (bought new 8/30/09)
2018 Arctic Fox 992 with an Onan 2500i "quiet" model generator

deltabravo

Spokane, WA

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Posted: 12/30/22 06:47am Link  |  Quote  |  Print  |  Notify Moderator

Mike in DE wrote:

I bought a 2022 Chevy 3500 6.6L Duramax Turbo Diesel


Dually or SRW?

Mike in DE

Delaware

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Posted: 12/30/22 08:12am Link  |  Quote  |  Print  |  Notify Moderator

My truck is an SRW, not a dually.

The data was over different routes. However, I made sure the starting and stopping elevation was always within 20 feet. Also, trans temp was always between 136 and 144. Finally, wind was typically at a minimum. Despite those relatively constant variables, the variation in the data was still pretty large. That's why I kept getting more data points. I will add that I found no difference in MPG as the outside temp changed. In fact, there was a slight downward trend with outside temp when I plotted the numbers for 65 and 70 mph.

Cummins12V98

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Posted: 12/30/22 09:48am Link  |  Quote  |  Print  |  Notify Moderator

Speed kills!!!


2015 RAM LongHorn 3500 Dually CrewCab 4X4 CUMMINS/AISIN RearAir 385HP/865TQ 4:10's
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Thermoguy

Graham, WA

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Posted: 12/30/22 11:17am Link  |  Quote  |  Print  |  Notify Moderator

I'm going to assume mileage gets better with some age. I have a 3/4 ton Duramax with similar size but heavier 5th wheel. I average about 13 or better when towing and typically at about 70mph.

Grit dog

Black Diamond, WA

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Posted: 12/30/22 11:17am Link  |  Quote  |  Print  |  Notify Moderator

Thanks for sharing. And not surprising. 50% fuel consumption increase giver take when towing a big sail has been the recipe forever. Nothing new.
Old Dmax and Cummins were in the 18/9 category around 70-75 mph (flat no wind). Newer Cummins is in the 14/7 range thanks to the lift, tires and too tall gears. Would be the same 18/9 if it was stock.
It does lend some credibility to those who claim 25mpg out of their big diesels. But what they forget to mention is they’re drivin miss daisy and p!ssing off the line of cars behind them who may actually have some where to be before their next birthday.


2016 Ram 2500, MotorOps.ca EFIlive tuned, 5” turbo back, 6" lift on 37s
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StirCrazy

Kamloops, BC, Canada

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Posted: 12/31/22 09:19am Link  |  Quote  |  Print  |  Notify Moderator

Grit dog wrote:


It does lend some credibility to those who claim 25mpg out of their big diesels. But what they forget to mention is they’re drivin miss daisy and p!ssing off the line of cars behind them who may actually have some where to be before their next birthday.


you know, the older I get the less I car about thoes cars.. they can pass when its safe or use the left lane to go around.. especialy with fuel prices these days haha


2014 F350 6.7 Platinum
2016 Cougar 330RBK
1991 Slumberqueen WS100

Cummins12V98

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Posted: 12/31/22 09:46am Link  |  Quote  |  Print  |  Notify Moderator

Thermoguy wrote:

I'm going to assume mileage gets better with some age. I have a 3/4 ton Duramax with similar size but heavier 5th wheel. I average about 13 or better when towing and typically at about 70mph.


13+ at 70??? I just have a hard time with some of these claims. If it were a sea level flat ground NO wind "MAYBE" if towing at 60.

My 98 12V was about as efficient as they get 22mpg commuting tank after tank filling to the top. ONE time I was 13+ North of the Grapevine along I-5. That was towing at 60 , my combo weighed 20k.

Fill your tanks to the TOP, use GPS to determine if ODO is off and if so compensate your miles. NOW report back after several tanks going both directions in many conditions.

35k combined double towing at 60mph from NW WA to Palm Springs, CA here are my mpg's at each fill to the TOP along the way 9.12, 8.26, 5.4 (slept with truck on high idle for 2.5 hrs), 10.0, 9.55, 7.35 (slept for 2 hours high idle with more miles on tank), 9.7 final fill. That is HONEST hand calc mileage. Never turned the truck off.

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* This post was edited 12/31/22 09:59am by Cummins12V98 *

wanderingbob

monticeeo, fla

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Posted: 12/31/22 09:51am Link  |  Quote  |  Print  |  Notify Moderator

My 2014 Ram CTD will get 16 mpg at 60 mph pulling a 21 foot TT . Twice on the Natchez Trace at the 40 mph I got 24 and 25 MPH .Speed spends !

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