Gas mileage or happy diesel engine & transmission !

[1231ChaseB]

A lot is said about what mileage we get ! In my case i wasn't getting any mileage anyway so i went for making the engine and Trans happy ! I tried the 63 or 64 MPH but every high spot i came to in the road the trans was downshifting and i personally don't like that ! I tried different speed's and found that for whatever reason if i went 67 the trans hardly ever down shift's ! That doesn't include serious hill's though ! Like going out of Kentucky into Tennessee on I-75 ! Something new to talk about !!!!
chaseb

 

[pegmikef]

I have ST Tires and they are rated for a max speed of 65, but I like to run a little under that and I haven't noticed that much down shifting. I usually run about 1700 and on a fairly steep hill it might get up to 22 - 23 hundred rpm. The down shifting usually occurs more often going down the hills. Course I have a pretty light rig < 9,000 lbs.

 

[Speedy]

I have towed wih speed in mind and also with RPMs and have found that keeping the engine in the sweet spot yields better mileage and less down shifts. The results are 1.5 to 2 MPG better.

 

[sjs731]

A lot is said about what mileage we get ! In my case i wasn't getting any mileage anyway so i went for making the engine and Trans happy ! I tried the 63 or 64 MPH but every high spot i came to in the road the trans was downshifting and i personally don't like that ! I tried different speed's and found that for whatever reason if i went 67 the trans hardly ever down shift's ! That doesn't include serious hill's though ! Like going out of Kentucky into Tennessee on I-75 ! Something new to talk about !!!!
chaseb

I hardly ever have downshifting at the speeds you are talking about except hills like you are talking about. We drove that stretch in August. I have a stock '07 Duramax.


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[NWILSON]

Several things will come into play here. The gear ratio of the differential will determine the load on the engine but, probably the biggest in new vehicles, is the programming of the engine control computer which is tasked with keeping emissions at the lowest level in any given condition!
The Tow/Haul mode may reduce some of the unwanted shiffing.

 

[porthole]

And you can't compare the Fords to GM's with speed/RPM's.

The trans ratios are quite different.
I have a chart of the 2011 big three but can't get to it until we are back on the power grid.


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[1231ChaseB]

By the way I Have a 2010 Cyclone 3912 and the truck is a 09 Silverado DRW 4WD extended cab with the 3:73 rear end
chaseb

 

[Bob&Patty]

What kind of fuel milage are you expecting? Your 3912 is a heavy trailer and your 09 is at its limit for towing. What is the GVW of your 3912?

 

[1231ChaseB]

I guess when i was experimenting i hoped for maybe 10 but i'm getting 8 and on a good day i might get 9 if the road is flat enough ! The GVW is 18,000 ! It's a load for this 3500 ! It actually does a great job and since i had a motor home before this i am used to getting 8 and 9 !
chaseb

 

[Sumo]

The Chevy has better power and torque at a little higher RPM. Source for this information can be found in the "King of the Hill" article by Diesel Power magazine.
I also get better mileage (11.8) with less downshifting at 67 MPH.

 

[jayandhisgals]

Were hulling a 3712 Cyclone GWV 18000k loaded with our 7.3L Ford diesel. Last week going to Branson Mo. big hills all the way we had to downshift into 3rd and could only run about 40mph up hill but got great gas milage around 13mpg. Havn't taken it out on flat land yet but I am sure we'll get even better milage then. Your doing good with that 3500 getting 9 mpg. You have a very large rig it's gonna cost ya to hull it. But well worth the $$, who else gets to camp in such comfort?

 

[tljack]

I am pulling a 2013 Heartland Road Warrior with a 2012 Silverado with Duamax and Allison. To date I have only 9,000 miles on it, mostly with towing. Today coming over the Cascade Mountains I got my normal 10.5. I was towing about 60 MPH. I usually tow at 65 mph. If I jump up to 75 I get 7.5 MPG.

 

[Hastey]

I have the same experience as everyone else with my D/A. I set the cruise control at 67-68 mph and that puts the tachometer between 2000 and 2100 and have very little downshift except on the big grades. I estimate 10 mpg but I never really check it. I burn 80 gal and fill it up and keep going. I try not to let them see me crying at the diesel pump.

 

[cemill]

I just traded trucks a month ago. Our last trip was to Mountain View, AR. Overall about 700 miles.
Some very hilly terrain some interstate bucking a quartering 15 to 20 mph wind.
Mileage average for the trip was 10.6 with the 2012 Duramax 3/4 ton.

 

[wolfrat1]

I have a 2012 silverado 3500hd crew cab 6.6L dually. With no trailer, I get 18 to 21 mpg at 65 mph on level pavement. With my 2012 bighorn 3610re it drops to 9.5 to 12.2 mph. I run it down to a 1/2 tank of gas. The fill ups aren't as much of shock to the wallet. I have to refill the def at about 6,000 miles. Also use Shell synthetic 5w40 and K&N air filter. A little cheater than Mobil 1 and IMHO, it performs the same. I used to run Mobil 1 and had no problems. It just came down to cost.

 

[mobilcastle]

If you run in the mountains all the time I think your MPG is going to drop some. My D/A gets about 11 MPG at 65 when I check it by hand. I run LT's. If I ran st's I would drop down to 60-I don't like st's on a heavy 5ver. In the big picture what is one or two MPG matter when you are having fun?

 

[JanAndBill]

With the trailer custom tune on my SCT controller I was averaging anywhere from 10.2 to 10.5 pulling a 3260 EL with a 2006 F350 dually. Replaced the oil cooler two weeks ago, and now the fan runs a lot less. My fuel mileage is running 10.7 to 11.0. Usually keep the speed range in the 65 to 67 which seems to be the ideal for this setup. Not towing, with the tuner set for street, I average anywhere from 16 to 18 depending on how hard I drive it. I try to research the fuel prices in route as I've found as much as $.20 a gallon difference and buy accordingly. Here's a link to a commercial site I've used for years there's no cost to use it or sign up requirements http://www.gocomchek.com/

 

[scottyb]

My 2007 3500HD D/A gets 13 - 15 empty. I bought it new and it now has 185K, but has a lot more engine hours, due to extensive idling and off roads driving. It has never achieved better than 16 empty. I have a log of every fillup and every oil or tire change, for tax purposes. It gets 8 - 8.5 pulling my Cyclone 4100. I pulled from Phoenix to Payson, AZ last fall and the water temp kept creeping up to 220 and the fan engaged on the 7% grades.

 

[Eddhuy]

With my 04 F350 6.0L, crew cab short bed diesel and a lighter trailer, Prowler Ti, I usually get low 14s but have gotten as high as 15.4 flat road and as low as 12.2 going into a head wind. It helped when I put on a 4" after market exhaust from the turbo back. I run less muffler and it is quieter. RPM, while in tow mode, dropped 250 RPM at same speed and I down shift less. I normally travel at 60 to 62 MPH.