STRANGE MPG
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Mountain Pass
Joined: Mar 2008
Posts: 125
Likes: 1
From: Chesapeake, Va
STRANGE MPG
I took a 415 mile trip (one way) last week, and set the cruise at about 61mph keeping my rpm under 2k thinking that would yield the best mpg. The best I got was 8.57mpg. On the way back I set the cruise at 65mph which put my rpm above 2k, and my return avg was 11.68mpg.
My truck has 4.10 gearing, so do you think I may need to drive above 2k rpm to get better mpg.
Has anyone figured out the true secret for the best mpg or is each truck unique?
My truck has 4.10 gearing, so do you think I may need to drive above 2k rpm to get better mpg.
Has anyone figured out the true secret for the best mpg or is each truck unique?
Postmaster
Joined: Nov 2006
Posts: 4,517
Likes: 3
From: SE Wyoming
61-65 is a bad zone for the torqueshifts I have found, they don't like to downshift at that speed and rpm and you have to speed up to get them to run below full boost when towing. I'd bet you were all but lugging it a lot if you were towing at that speed. It is my one gripe about them. I've noticed with the 6.0L, 6.4L and 6.8L all with different rears.
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Mountain Pass
Joined: Mar 2008
Posts: 125
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From: Chesapeake, Va
Best I can remember it was calm. I stop at truck stops and use cetane boost every fill up. I'll probably have to average it out at that speed to get the real mpg. I have always towed at a lower speed, and thought it was wierd. I have 58k on it now, and that is probably the best mpg I will get towing.
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Mountain Pass
Joined: Mar 2008
Posts: 125
Likes: 1
From: Chesapeake, Va
61-65 is a bad zone for the torqueshifts I have found, they don't like to downshift at that speed and rpm and you have to speed up to get them to run below full boost when towing. I'd bet you were all but lugging it a lot if you were towing at that speed. It is my one gripe about them. I've noticed with the 6.0L, 6.4L and 6.8L all with different rears.
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Joined: Aug 2008
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From: Frederick, MD
I tow right at 65 mph and usually anywhere from 7-9 depending upon terrian. But that is heavy towing.
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Laughing Gas
Joined: Feb 2007
Posts: 950
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From: Waco, Texas
Yep, I tow at 65 and it will average between 9 and 10 that is at around 1800 rpm running 3.73's. If I try towing at 60 which is about 1600 it goes to about 8. Don't tow over 65 as I am running ST tires on the trailer.
It seems that the sweet spot, empty or towing is at 1875 rpm or so. Thats gets me real close to 70. Anything over 70 empty, the mileage goes down rather quick.
It seems that the sweet spot, empty or towing is at 1875 rpm or so. Thats gets me real close to 70. Anything over 70 empty, the mileage goes down rather quick.
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Logistics Pro
Joined: Nov 2001
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From: Georgia
My 4.30 does best ar 1950 just below 60 MPH, probably 59.5 or so. Since the EPA's experiment fell off I've gotten 10 or so on some pretty long runs but I think if I drive it a lot next summer I'll end up averaging 9. something.
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Mountain Pass
Joined: Mar 2008
Posts: 125
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From: Chesapeake, Va
My gross weight is about 23k, so it's heavy. I just cant figure why the mpg would be better going faster?
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Mountain Pass
Joined: Mar 2008
Posts: 125
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From: Chesapeake, Va
Our truck are pretty much the same in weight. I think I may have to run a few more times at that speed to get a better average. With winter blend it may go down, but then again who knows?
Elder User
Joined: Aug 2004
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From: Edmond, OK
I too have 4.10 gears; my dually gets best mileage at 60-62 MPH (@ or below 2,000 RPM) when solo, with MPG usually north of 15.5. Running 70 MPH on Interstate with about a 50/50 mix city/HW I am 12-13 MPG. Running 60-62 MPH on HW's w/ 50/50 city/HW will jump me up to 14-15 MPG overall. All solo w/ no towing.
Towing fiver puts me in the 8-9.5 MPG range. Car hauler or tractor on trailer usually north of 10 mpg.
I can run 70 mph towing the fifth wheel and between OKC and Vian and it does not downshift on I-40. The 6.0's I had would with the 3.73 gears; but my son-in-law's wouldn't if running 75+.
My fiver tires are rated for 70 MPH; but generally I run 60 when pulling unless it makes sense because of traffic to run 70.
Towing fiver puts me in the 8-9.5 MPG range. Car hauler or tractor on trailer usually north of 10 mpg.
I can run 70 mph towing the fifth wheel and between OKC and Vian and it does not downshift on I-40. The 6.0's I had would with the 3.73 gears; but my son-in-law's wouldn't if running 75+.
My fiver tires are rated for 70 MPH; but generally I run 60 when pulling unless it makes sense because of traffic to run 70.
Postmaster
Joined: Nov 2006
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From: SE Wyoming
I don't tow for mileage, usually 2-3mph over the limit so either 67-68 or 77-78. Problem arises on 65mph roads when I hit a hill and the speed backs off to 65 then I have to let it drop to about 59mph so it will downshift and run back up to 65 to upshift. Just some crappy programing where it won't downshift between 60-65mph so it is a dead zone.
I was towing around 24K GCW and then a 27K GCW and on the second heavier trip slowed down to about 70mph and it seemed to get just as bad if not worse mileage, I noticed it stayed at max boost instead of downshifting a lot more than when I was doing 75mph+ with the first load. I also had a regen from hell that just wouldn't end that didn't help on both trips.
I was towing around 24K GCW and then a 27K GCW and on the second heavier trip slowed down to about 70mph and it seemed to get just as bad if not worse mileage, I noticed it stayed at max boost instead of downshifting a lot more than when I was doing 75mph+ with the first load. I also had a regen from hell that just wouldn't end that didn't help on both trips.
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Mountain Pass
Joined: Mar 2008
Posts: 125
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From: Chesapeake, Va
I will probably start traveling at 65mph and see how it goes. It can't be any worse than I'm currently getting, so why not give it a shot. Over the next few trips I will post my findings.
Logistics Pro
Joined: Nov 2001
Posts: 3,788
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From: Georgia
Yeah, my experience has been that the MPGs are all over the place. I made a long trip last summer, ATL out to Seattle down to California and back east on I70 to OK then down to I40 and home. I kept very good records and had runs with the trailer on from a low of 6.5 to a high of 9.2. They were all over the place. I don't have my book with me but I think the average towing fror the whole trip was in the mid 8s. The MPGs are impacted by the terrain and the wind way more than my 7.3 was. With the DPF off I've made a couple trips over known routes and the truck seems to have gained close to 1 MPG. Not much but if it holds up it will represent a 12% increase. That's probably all I can hope for given the 4.30 axle and the Total weight of 25,000 lbs +/-.
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