Diesel Fuel Economy Comparison- Economy Challenge

Diesel Fuel Is Expensive. Less Than A Year Ago It Was Cheaper than gasoline, and now it is almost 30% more than unleaded. High fuel prices are something that we're going to have to come to terms with; and to help with that, we tested five vehicles on the same day, on the same route, and at the same speed. Not only would we get results, but we would get to compare old versus new, two-wheel drive vs. four-wheel drive, and emissions vs. no emissions. Older Dodge Rams ('89-'93) are notorious for being fuel mileage champs, so we picked up two for the test-our own Project Rust Bucket, which is two-wheel drive with a three-speed automatic, and Ken deVoogdt's '93 Dodge, which is a 4x4 with a five-speed manual transmission. Ken's truck is also lifted and on taller and wider tires than stock, which certainly affects mileage. For newer vehicles, we had an '07 LMM truck that was four-wheel drive, and a two-wheel-drive '07 LBZ. The LMM had EFILive, which was used to turn off the factory regeneration sequence during our drive, and the LBZ had an "economy" tune loaded because it was a Pacific Performance Engineering (PPE) shop truck. We also brought our '07 Jeep Grand Cherokee CRD along, which had the advantage of having the smallest engine, but also had a lift, different tires, all-wheel drive, and full emissions equipment. Would technology prevail? Could the lighter weight of the old trucks be an advantage? Would the Jeep take the win despite of its emissions and drivetrain limitations? We won't spoil the ending just yet, but we will tell you that you may be surprised by the results.

To start, we went over to the local Chevron station and filled up all the vehicles. There were some shenanigans, such as truck rocking and topping off (mostly by Associate Editor Jason Sands in Rust Bucket), but not too much of an effort was made to do anything sneaky. In fact, everyone was running the same tune and tire pressure as they would any other day, giving the test a "real world" flavor. From Los Angeles, the trip traveled up the 101 Freeway along the coast toward San Luis Obispo, a 181-mile drive that would test our mileage theories. We had planned to average about 65 mph, but hit some traffic that slowed us to 35-50 mph on some sections because it was Memorial Day weekend. This actually might have helped our mileage case, as our average speed ended up somewhere around 60 mph. Besides driving slow, almost everyone admitted to driving "to win it," which meant no quick accelerating and coasting down hills (generally driving like Prius owners instead of diesel truck enthusiasts). Mother Nature was determined to counter our driving techniques, however, and sent a rainstorm our way. Water on the road makes for more friction, which makes for worse mileage. Still, after about 60 miles it cleared up nicely, and we were able to enjoy the rest of the drive up the coast with clear skies.