Has anyone else noticed better highway MPG at 85-90+MPH?

spoolin'up · 07-01-2008, 07:52 PM

I've noticed that my 6.7 seems to get better mileage if I'm 'breaking the law, breaking the law', than if I'm going a normal 75+/-. Has anyone else noticed this? I think it might be related to the flash I have which seems to be more oriented towards 'soft' regens. I've never seen a 'cat full' message on the overhead or had to go through a hard regen in 25,000 miles, although I did smoke a DPF (and had the ECU flashed) at 10,000. Mine was a early (about as early as you can get) build. My theory is that if you're really givin' it to her the DPF stays hot enough that it never gets plugged.... Therefore it doesn't even go into soft regen, it's just burning hot enough to stay clean. Does this make sense to anyone else, or am I just making up excuses to speed?

__________________
2007.5 3500 Laramie MegaCab 4x4 SRW 68RFE

Last edited by spoolin'up : 07-01-2008 at 07:56 PM.

LSmith · 07-01-2008, 07:59 PM

I haven't tried 85 MPH, but I do seem to get better mileage -- about 1 MPG -- at 75 (1900 RPM) vs 68 (1700 RPM).

__________________
2007.5 2500 4X4 Quad Cab 6.7L
Len

juanjo322 · 07-01-2008, 07:59 PM

I get better when i stay steady on 65mph, anything over that it tends to drop and i have 3.73's

__________________
2008 6.7l F/E & R/E Replacement 70gal aux fuel tank with tool box, headache rack,Rhino liner, 12k Warn DF, Edge Juice w/attitude, TS MP-8, S&B CAI, 5" H&S TBE, EGR??

. Snow Performance Stage III MPG Max. Next Turbo, intercooler, manifold..

spoolin'up · 07-01-2008, 08:05 PM

hmm.... people start shooting if you go much under 70 on the expressway around here, but maybe if fuel goes up a bit more I'll have to give it a try some day... On the 5.9s, I always thought the sweet spot was about 2200 RPMs.... on a 6.7 with tall gears that's about 85...

__________________
2007.5 3500 Laramie MegaCab 4x4 SRW 68RFE

***Compcowboy*** · 07-01-2008, 09:13 PM

I get about 2-3 MPG better @ 65 then 75. Not sure about higher.

__________________
??? Hp ???? Tq - 2007 6.7 TWIN TURBO 2500 Bighorn 4x4 6-spd Manual, Airdog 150, ARP Head Studs, Bullydog PMT, TS MP-8, Airbags with Dual Control Air Comp., H&S Delete & Downpipe, What EGR?, Valair Dual Disk, Amsoil Bmk-11 Bypass, 295/70/R17 Toyos on Walker Evans Wheels,6" Aussies & Hushpower Muffler & DiProcol Gauges & 120HP nozzles (on the way) Thanks to Wally At FTEDiesel!!!!!

Ram3500Dually · 07-01-2008, 09:19 PM

1800 @ 68 MPH gives me the best hand calculated fuel mileage. It drops after that and the faster I go the faster it drops.

__________________

2008 Ram 3500 CTD 6.7/68RE/3:73 LSD
Previous Rams 90 CC Dually, 94 RC LB, 95 CC SB, 98 QC Dually, 00 QC Dually, 01 QC Off Road, 03 QC Dually, 05 QC Dually REAL TRUCKS DON'T HAVE SPARK PLUGS

Eveready77 · 07-01-2008, 09:23 PM

On my 5.9 I have noticed a bit of difference at faster speeds too. Also seems like a good hard start from a red light every now and then gives me a little bump too. I can't verify this by hand numbers as I just started noticing it recently, but it shows up on the overhead "feel good" computer.

__________________
2007 2500, Thunder Road, Quad-cab, SLT, 5.9l, 4x4, short bed, leather seats and chicken lights,35k mi. new to me. Stock for now.

07-01-2008, 07:52 PM	#1 (permalink)
spoolin'up Cummins Fanatic Join Date: Jun 2008 Location: Rustville, MI Posts: 128 spoolin'up's Truck Pics	Has anyone else noticed better highway MPG at 85-90+MPH? I've noticed that my 6.7 seems to get better mileage if I'm 'breaking the law, breaking the law', than if I'm going a normal 75+/-. Has anyone else noticed this? I think it might be related to the flash I have which seems to be more oriented towards 'soft' regens. I've never seen a 'cat full' message on the overhead or had to go through a hard regen in 25,000 miles, although I did smoke a DPF (and had the ECU flashed) at 10,000. Mine was a early (about as early as you can get) build. My theory is that if you're really givin' it to her the DPF stays hot enough that it never gets plugged.... Therefore it doesn't even go into soft regen, it's just burning hot enough to stay clean. Does this make sense to anyone else, or am I just making up excuses to speed? __________________ 2007.5 3500 Laramie MegaCab 4x4 SRW 68RFE Last edited by spoolin'up : 07-01-2008 at 07:56 PM.

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07-01-2008, 07:59 PM	#2 (permalink)
LSmith Cummins Fanatic Join Date: Jun 2008 Location: Alabama Posts: 111 LSmith's Truck Pics	I haven't tried 85 MPH, but I do seem to get better mileage -- about 1 MPG -- at 75 (1900 RPM) vs 68 (1700 RPM). __________________ 2007.5 2500 4X4 Quad Cab 6.7L Len

07-01-2008, 07:59 PM	#3 (permalink)
juanjo322 Cummins Nut Join Date: Jun 2007 Location: tx Posts: 314 juanjo322's Truck Pics	I get better when i stay steady on 65mph, anything over that it tends to drop and i have 3.73's __________________ 2008 6.7l F/E & R/E Replacement 70gal aux fuel tank with tool box, headache rack,Rhino liner, 12k Warn DF, Edge Juice w/attitude, TS MP-8, S&B CAI, 5" H&S TBE, EGR?? . Snow Performance Stage III MPG Max. Next Turbo, intercooler, manifold..

07-01-2008, 08:05 PM	#4 (permalink)
spoolin'up Cummins Fanatic Join Date: Jun 2008 Location: Rustville, MI Posts: 128 spoolin'up's Truck Pics	hmm.... people start shooting if you go much under 70 on the expressway around here, but maybe if fuel goes up a bit more I'll have to give it a try some day... On the 5.9s, I always thought the sweet spot was about 2200 RPMs.... on a 6.7 with tall gears that's about 85... __________________ 2007.5 3500 Laramie MegaCab 4x4 SRW 68RFE

07-01-2008, 09:13 PM	#5 (permalink)
*Compcowboy* 1st 6.7 with Twins Join Date: Nov 2007 Location: Kennewick, Wa Posts: 3,543 Compcowboy's Truck Pics	I get about 2-3 MPG better @ 65 then 75. Not sure about higher. __________________ ??? Hp ???? Tq - 2007 6.7 TWIN TURBO 2500 Bighorn 4x4 6-spd Manual, Airdog 150, ARP Head Studs, Bullydog PMT, TS MP-8, Airbags with Dual Control Air Comp., H&S Delete & Downpipe, What EGR?, Valair Dual Disk, Amsoil Bmk-11 Bypass, 295/70/R17 Toyos on Walker Evans Wheels,6" Aussies & Hushpower Muffler & DiProcol Gauges & 120HP nozzles (on the way) Thanks to Wally At FTEDiesel!!!!!

07-01-2008, 09:19 PM	#6 (permalink)
Ram3500Dually Diesel Head Join Date: Feb 2007 Location: Windsor Ontario Canada Posts: 2,686 Ram3500Dually's Truck Pics	1800 @ 68 MPH gives me the best hand calculated fuel mileage. It drops after that and the faster I go the faster it drops. __________________ 2008 Ram 3500 CTD 6.7/68RE/3:73 LSD Previous Rams 90 CC Dually, 94 RC LB, 95 CC SB, 98 QC Dually, 00 QC Dually, 01 QC Off Road, 03 QC Dually, 05 QC Dually REAL TRUCKS DON'T HAVE SPARK PLUGS

07-01-2008, 09:23 PM	#7 (permalink)
Eveready77 Newbie Join Date: Apr 2008 Location: Chattanooga Tn. Posts: 15 Eveready77's Truck Pics	On my 5.9 I have noticed a bit of difference at faster speeds too. Also seems like a good hard start from a red light every now and then gives me a little bump too. I can't verify this by hand numbers as I just started noticing it recently, but it shows up on the overhead "feel good" computer. __________________ 2007 2500, Thunder Road, Quad-cab, SLT, 5.9l, 4x4, short bed, leather seats and chicken lights,35k mi. new to me. Stock for now.