The only rivalry in Michigan as intense as the one between the HD manufacturers is the spirited competition between the University of Michigan in Ann Arbor and Michigan State University in East Lansing. That’s why it made sense to drive the trucks between the two cities for our fuel economy challenge.
The trucks ran the approximately 150-mile circuit twice, for a total of around 300 miles, once unloaded and once towing a trailer. Tow/haul mode was used when the trucks were towing.
We started our test at the Pilot Truck Stop in Dexter, Mich. The same diesel and gasoline pumps were used for both loop fill-ups, with the same designated “filler” at the diesel and gasoline nozzles, using the same procedures and techniques.
Each truck’s fuel tank was filled to visual sight of liquid at or very near the top of the filler tube. Amounts of fuel were recorded, as well as odometer, tripometer and vehicle mpg computer information. All vehicles were reset at the beginning of the fuel economy test at the pump, and also reset at the end of the first loop at the same pump.
Completed information is presented in two ways below. First, information from each truck is recorded in two charts from both loop 1 and loop 2. Second, vehicles are grouped by class (gas, SRW diesels, DRW diesels) and charted in head-to-head comparison format, both with and without trailers.
How rigorous were we with measuring our diesel fuel economy? We had techs from each of the manufacturers trigger manual service regenerations to clean out the trucks’ diesel particulate filters.
DPFs trap soot, a byproduct of diesel’s lean combustion process because not all of the fuel is burned. After a while, depending on workload and driving distance, the DPF becomes full and needs to be cleaned out, much like a self-cleaning oven. Extra diesel fuel is injected into the exhaust stream to boost temperatures in the DPF to more than 1,000 degrees, incinerating the trapped soot. That process can require up to six-tenths of a gallon of diesel – an amount large enough to impact our fuel economy measurements on a 300-mile drive. That’s why we started each truck with a clean DPF.
We attempted to measure consumption of urea, or diesel exhaust fluid, for the first time. The harder a truck works, the more DEF that is consumed. At the Pilot station, it cost $2.99 a gallon at the pump and $5.99 a gallon by the bottle. Before we started our driving loop, we topped off the Ford and GM trucks – again, the Ram HD trucks are DEF-free – and measured their consumption at the end of both loops. For those interested in calculating their cost per mile, this new fluid addition must be included.
Total DEF measurements were conducted for the test, which included topping off at the beginning of the day, refilling at the end of the day and calculating usage.
Fuel economy and DEF consumption (where applicable) data is displayed below.
Update #1 August-17-2010 10:29 am PDT:
Thanks to a tip from commenter "Joe," we've updated the fuel economy commentary and tables below.
Unloaded and Loaded fuel economy calculations are unchanged from their original figures. Each took the distance traveled (miles) divided by fuel consumed (gallons) to calculate miles per gallon.
However, the combined fuel economy calculation that averaged the loaded and unloaded mpg calculations has been changed to an accurate formula that takes the total distance traveled during both legs and divides it by the total fuel consumed — the same way we calculated discrete unloaded and loaded fuel economy.
For example, using the old method of calculating combined fuel economy, the Chevy Silverado 6.0 achieved 14.10 mpg without a trailer and 10.16 mpg while towing and the average of those two figures was 12.13 mpg — an inaccurate way to calculate combined fuel economy. The new method takes the 318.41-mile total distance driven and divides it by 26.97 gallons (11.28 gallons unloaded + 15.69 gallons loaded) of fuel consumed to calculate an accurate figure of 11.81 mpg combined.
I regret the error and apologize that it will change the best combined fuel economy for the gas single-rear-wheel trucks from the Ram to the Silverado, and the diesel SRW trucks from the Silverado to the F-250. The diesel dual-rear-wheel trucks are unchanged. Again, it has no effect on the individual towing and unloaded mpg figures.
This update has no effect on how we scored the trucks, as the fuel economy score was based solely on how each truck performed in loaded and unloaded testing. Combined fuel economy was not a factor in the final score.
Again, thanks to Joe for spotting the inaccuracy and raising the question about it. This is one reason why we share all of the data we collect with our readers.
- Mike Levine
For the three-quarter-ton gassers, the Chevrolet Silverado 6.0 was most fuel-efficient in combined driving, returning 11.81 mpg during the 300-mile drive, even though it never had the best fuel economy towing or unloaded. Unloaded, the Hemi-powered Ram 2500 returned a remarkable 15.04 mpg, likely due to its five-speed transmission and first overdrive that’s available in fourth gear, compared with fifth gear in the six-speed trucks. The Ford F-250 6.2 was the most efficient gas truck while trailering, averaging 10.86 mpg.
The Ford F-250 6.7 diesel was the most fuel-efficient three-quarter-ton oil burner, edging out the Silverado by just .05 gallons during combined loaded and unloaded driving. The Chevy Silverado 2500 came closest of any truck to breaking the 20 mpg mark during unloaded driving, at 19.66 mpg. The Ford F-250 had the best fuel economy towing at 13.91 mpg.
The Ford F-350 one-ton scored the best combined fuel economy number among the one-tons at 14.64 mpg. Without a trailer hanging off the back, the Sierra had the best fuel economy while the Super Duty was the most efficient of the three trucks pulling the six-ton trailer.
Amongst the three-quarter and one-ton diesels, the Ford trucks returned the best combined mileage even though the GM twins did best unloaded and the Super Duty's pulling.
Given how poorly the GMC Sierra 3500 Denali did relative to the three-quarter-ton Silverado under load and the F-350, we suspect it might have gone through regeneration when we were towing, even though we'd done a manual regen before the trip started. GM diesels can go a maximum of 750 miles before they have to regenerate their DPFs.