King of Beasts: Fuel Economy

5 Group Highway II

Photography by Evan Sears

Although no one is likely buying these heavy-hauling Kings of Beasts based purely on fuel economy, we know it is a real issue for every truck buyer.

We filled up our test trucks at least 10 times during our 1,600-mile journey from Dillon, Colo., to Las Vegas, past Flagstaff, Ariz., up to Moab, Utah, and finally back to Dillon. Our route led us to nine different fueling stations, many of which were populated by curious onlookers. It's not every day, apparently, that you see identically equipped bright orange brand-new flatbed trailers and two new, fully optioned 2013 one-ton pickups.

To provide accurate and informative fuel mileage numbers, we haven't included the two fill-ups after our Davis Dam acceleration and exhaust brake testing, as well as the fill-ups after the Eisenhower Pass acceleration and exhaust brake testing. As you would suspect, those runs produced much lower average mileage numbers due to the nature of the tests. Many runs were done repeatedly at wide-open throttle, certainly not ideal for fuel-economy data collection.

No Surprises?

Over the 1,500 remaining miles that we logged on the trucks with their 24,000-plus-pound trailers, the Ram 3500 HD recorded 8.08 mpg while the Ford F-450 averaged 7.95 mpg. Statistically, this is a dead heat, as the two numbers are within one percentage point of each other. Historically, the Cummins has done poorly in tests versus both the Power Stroke and the Duramax turbo-diesels.

Neither truck's onboard trip computer's average mileage information was particularly accurate, with the Ford's being the most optimistic "guesstimator" of calculated fuel mileage. The Ram's computer seemed much more accurate, and it even shortchanged itself on one fill-up calculation. The Ford's computer, if you added up all the fill-up readouts and averaged them, calculated the Power Stroke average at 8.5 mpg (when actual mpg was 8.0), while the Ram's computer calculated the Cummins' average to be 8.2 mpg (our results showed 8.1 mpg). 

On our full-length trip, the Ram recorded the best tank average at 10.3 mpg (its worst was 7.5 mpg); the Ford's best was 9.6 mpg (its worst was 7.0 mpg).

KOB MPG Route II

KOB_MPG_Final

Overview | Acceleration | Braking | Fuel Economy | Comfort and Squats | Results

Comments

The addition of DEF is why the Ram is suddenly competitive in fuel economy.

Good job. Ram!!

What sucks almost as much fuel as fast as a Ford 460? A Ford 6.7 No Power Joke!

You have to remember that these trucks are pulling heavy loads. These results fit with the laws of physics - it takes x amount of energy to move y mass.

Lou,

You are absolutely right, but the 460 doesn't have to waste fuel burning in a Diesel Particulate filter.

That's absolutely wasted fuel, in addition there is the cost of the Urea.

@buddyIam - these trucks under full load are not going to need much in the way of regen. The soot traps are going to be kept plenty hot. Regen will eat up lots of gas if a guy buys one of these trucks and 20 days of the month goes back and forth to work with the an empty truck which then sits in the staff parking lot for 8 hours.

Lou,

This was only a ten minute pull, I'm not sure that it would get the converter all that hot. In addition following the climb they spent more time coasting down the hill than climbing it.

The loss of speed at the top of the hill would make one think that the Ford's turbo's cut back on air. That means unless the computer cut way back on fuel a bunch of soot was produced. Those soot particles are the particulates that have to be burned out of the converter. Running flat ground for a long period without load would cause a clean burn in the catalyst. Pretty much the opposite of what your are figuring.

The fact that the trucks use a bunch of Urea under load would seem to support my thinking.

Not saying you are wrong. I'm just saying:

To bad we were not there to help with this test. :>)

I have a 2009 Laramie 3500 short bed quad Cummins. It has gone through a regeneration cycle a grand total of 3 times in its lifetime. Running at highway speed keeps the DPF clean and regeneration free. I figure I have wasted very little fuel on regeneration over the 40K miles I have on the truck. I have no opinion on whether regeneration or urea injection is the best method of keeping a diesel running green, but it seems there is rather modest cost involved with each strategy. The DEF is cheap, and if you run the speed limit on the highway it never seems to need a regeneration cycle. Looks like a wash to me.

Good job on dodge's part they finally are worth comparing. They really stepped up with the increased horsepower and torque. DEF has really helped performance as without it hp numbers had to be lower to meet emissions. I cant believe how little some people know about there OWN vechicle. I have heard a few dodge owners talk about how there 1-4 year old particulate trucks and how they have only went through regen a couple times. This is NOT possible. You can drive your truck as easy as you want highway cruising or not its GOING to burn out approx once every 4-600 miles if your using it as a truck maby a bit better if conditions are right and no towing etc.

@buddylam

Indeed, the Ford was running out of air at the top of the mountain (mostly because its fragile little single-shaft-sequential turbo was having trouble pumping air at that altitude without overspeeding), but believe me, the truck was NOT sooting up its DPF as a result. The truck is much smarter than that. It monitors its air intake with a multitude of sensors including MAF, AIT, and of course boost, and fuels accordingly to maintain the correct fuel/air mixture, avoiding the "sooty scenario" you theorized.

Also, I can guarantee you flying up a mountain at full throttle and full load for 12 minutes will get the EGT and DPF MORE than hot enough to passively regenerate. Simply flooring a truck on level ground can get the EGTs to the 1000*F in seconds. Add on the fact they are towing at max payload up an average 6% grade for 12 minutes, and the DPFs in both of these trucks are both easily passively regenerating themselves, which helps save a bit of fuel.

Happy dieseling!



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