2010 F-350 Diesel Poor Mileage - Page 2 - Montana Owners Club

**Carl n Susan** · 03-17-2011, 08:48 AM

Our 2008 6.4L F250 towing a fully loaded 2955 get a consistent 9-10 MPG hand calculated. The lie-o-meter is .5 to 1 MPG higher. I have never averaged 5 MPG despite towing over some pretty significant hills. I recently drove 300 miles from Bakersfield to Sacramento on I-5 at 65 MPH into a 35 MPH (with gusts to 50 MPH) head wind! Not optimal conditions for good mileage. The resultant 7 MPG was the worst I have ever recorded and I have tracked every tank of fuel consumed.

5 MPG means your friend has a significant problem.

AJH · 03-19-2011, 05:33 PM

5 MPG.. Wow But I must I this past winter I stayed in Fl and I was getting 12 to 14 MPG when out west in the higher elevations (not mountains) I was getting less then 12.

Trailer Trash 2 · 03-19-2011, 07:42 PM

My old ford 7.3 PSD got 10.5 mpg and 11.5 with a tail wind on a flat. 9.5 pulling a hard hill with 4.10 gears @ 62 mph. I think it doesn't matter what you got they will all be very close to those numbers. not pulling I got 16 mph @ 60 mph. that is not a 6.0 or a 6.3 those I would think should get much better milage being a new type engin.

kingdaddy · 03-22-2011, 05:51 AM

I am very happy with my mileage numbers after reading all these posts! My impression is that the Cummins do tend to do a bit better on mileage depending on variables of course.
Maybe it's the two fewer cylinders?

Anyway, I can get consistent 19 mpg unloaded (hand calculated, lie-o-meter shows about 20). On my recent trip to pick up the Monty in OK. I averaged right around 19.2 and a LOT of 75 mph running across I-40.
My truck is not stock (power and efficiency ehancements) and is geared pretty high. 3.73 gears but with 34.5" tires give me an effective ratio of around 3.55.
At 65 mph, I am only turning 1,650 rpm, really in the "sweet spot".
The truck loves to cruise at 75, still only turning around 1,750-1,800.
Very hard to tow at 55 mph, the engine is just turning too slow and the EGTs tend to run high unless I take it out of O.D.
After the return trip with the new trailer, I had just over 13 mpg over 1,550 miles with the trailer. Some headwinds too and this was a lot of 60-65 mph towing.
Sorry guys, really not trying to rub it in...one reason I went with the '06 Cummins- no DPF and better mileage from what I had heard. So far so good...

harryd2 · 03-22-2011, 08:47 AM

check gear ratio if 4.88 too bad, lots of power no mileage

eastridges · 03-22-2011, 12:08 PM

I get about 12.5mpg normally while towing on flat road, hilly about 9mpg. I could get even worse if I shotgun start and have alot of stop and go. Light on the pedal, doesn't make a whole lot of difference when you stop for the night unless your traveling 700 miles a day.

CamillaMichael · 03-23-2011, 10:18 AM

Quote:

quote:Originally posted by kingdaddy

I am very happy with my mileage numbers after reading all these posts! My impression is that the Cummins do tend to do a bit better on mileage depending on variables of course.
Maybe it's the two fewer cylinders?

Anyway, I can get consistent 19 mpg unloaded (hand calculated, lie-o-meter shows about 20). On my recent trip to pick up the Monty in OK. I averaged right around 19.2 and a LOT of 75 mph running across I-40.
My truck is not stock (power and efficiency ehancements) and is geared pretty high. 3.73 gears but with 34.5" tires give me an effective ratio of around 3.55.
At 65 mph, I am only turning 1,650 rpm, really in the "sweet spot".
The truck loves to cruise at 75, still only turning around 1,750-1,800.
Very hard to tow at 55 mph, the engine is just turning too slow and the EGTs tend to run high unless I take it out of O.D.
After the return trip with the new trailer, I had just over 13 mpg over 1,550 miles with the trailer. Some headwinds too and this was a lot of 60-65 mph towing.
Sorry guys, really not trying to rub it in...one reason I went with the '06 Cummins- no DPF and better mileage from what I had heard. So far so good...

34.5" tires??? Those are BIG!

mlh · 03-23-2011, 03:14 PM

Mike how much HP is your Dodge pulling?
Michael your tires are 33.4 inches if you have the 18 inch wheels slightly larger if you have the 20s.
Lynwood

carlson · 03-27-2011, 07:48 AM

I have an 08 with the 6.4, and I pull a Big Sky at roughly 16000 lbs loaded. I get about 11 at 65 MPH. If he's onmly getting 5 on fairly flat ground, he needs to either lighten his load, lighten his foot on the throttle, or see his dealer ASAP, as something else is bad wrong.
IMHO!!

kingdaddy · 03-27-2011, 12:42 PM

Yes I am running 315/70 17 tires which measure out to right around 34-34.5" diameter.

As far as HP, I have my Smarty Jr. set at the lower tune and with the other mods I figure around 400-425 HP and probably about 7-800 lb/ft of torque. I could easily set the tuner to max. performance for around 500 HP and more torque, but the transmission would suffer especially when towing. These Cummins engines can be tuned for some amazing power outputs!

Careful tuning and well chosen mods (and conservative driving) can produce more HP and better mileage...up to a point.

klash · 03-27-2011, 05:53 PM

Here is the data on our rig. First of all we are Canadians, so all our figures are for the Canadian gallon which is slightly larger. All calculations are by hand. Sometimes I like the numbers on the lie-o-meter, but we know that they are not accurate. We always use self
serve stations and fill to first auto shut off only.
We have a 2011 GMC 3500 HD, crew cab, short box single rear wheel, and we currently have
about 7,000 miles on the truck. We had a 2003 Duramax, and the new truck is totally awesome, loaded with lots of good stuff, tons of smooth power, very quiet and quite
efficient.
We are currently in Desert Hot Springs, CA and beginning our trip north tomorrow the 28th of March.
We have a 2007 Montana 2955RL that weighs in at 12,000 lbs. On the way down we were getting 12 to 13 miles to the gallon in the mountains. Once we arrived in Sacramento it went up to 15 mpg. We have had 24.8 mpg empty, at 65 mph in cruise.
We NEVER tow over 55 mph. After all it is the law here in California. After towing over 250,000 miles in 39 states and 10 Canadian provinces, this is the speed we have found most comfortable. Is is easy on the machinery, and easy on the body. I know I can stop sooner, we enjoy the scenery and feel very relaxed and fresh when we get to our destination.
I am 72 years of age, and I don't drive slow because of my age. After all our years of towing I have learned that 55 mph is the most efficient speed for the trucks we have owned. (Two GMC 2500 gassers, a 2003 2500 HD duramax, and now the 2011 3500 HD duramax. We also have a rule in our rig, no more than 250 miles a day.
At 55 mph the new Duramax is running sweetly at 1,350 rpm's and it will go like that
day in and day out.
I realize we all have a different mission, so it is quite possible that what works for us, doesn't necessarily work for others.
We see a lot of other trucks and fifth wheels flying by us. I guess in the end we all get to
our planned destinations, but with different priorities.
Lastly, our 2003 GMC 2500 HD duramax towing the same trailer was giving us 15 to 16 miles per gallon last summer when we drove across the entire continent from east to west and back. Traveling empty we once had 30.8 miles per gallon. This truck had 110,00 miles on it when we gave it to our son last summer.
I truly hope that our 2011 will see improved mileage when it is properly broke in.

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