TECHNICAL Q&A

PROBLEMS & FIXES

My basic question is: Is the fuel economy advantage for diesel engines confined to the newer more efficient engines or have the diesel engines always outperformed (with respect to fuel economy) gas engines?

I recently purchased a 2017 GMC work truck with the Duramax diesel engine. I am thrilled with the fuel economy versus the same truck with a gas engine. When I load this truck down, it seems to have very little effect on the fuel economy. It’ll take a few more tanks of fuel to know for sure, but the truck has delivered 18 to 19 mpg during local driving in the short time I’ve owned it.

I am now looking at purchasing a second work truck. The one I’m looking at is considerably older. It is a 2000 Ford F-250 2WD with a 7.3L Power Stroke, and currently has 169,000 miles on the odometer. It’s actually a retired electrical power-line utility truck (w/utility box). I need to know what sort of fuel economy to expect from this older diesel engine. If this 2000 vehicle was a standard ¾-ton truck, could I expect to get 16 mpg or better?

Kyle Nesbit Eugene, OR

Diesel fuel and compression ignition combine to produce a fuel efficiency advantage over an equivalently sized and powered gas engine. That fuel efficiency advantage could range from 20 to as much as 100 percent depending on how old or new the engine comparison might be. For example, a 6.2L gas V8 in GM’S newest trucks might produce 8 mpg while towing a 10,000-pound travel trailer, while the Duramax could produce 12 mpg (or a little more or less). Plus, the diesel engine will tow that trailer with a whole lot less effort. The diesel fuel economy advantage will be somewhat lessened when driven without a load. GM’S latest 6.2L gas engine is EPA rated at 14 mpg city and 20 highway unloaded. But comparing a 2000 7.3L PSD to a current gas engine isn’t quite apples to apples.

The following two engines were available in the 2000 model year Ford heavyduty pickups. The first one is a gas engine and the second a turbo diesel. Real world fuel economy reports peg the V10 gasser at 10 to 12 mpg highway and 8 mpg or so towing. The Powerstroke should produce 14 to 16 mpg highway and 10 to 12-mpg towing. 6.8L (415 cu.in.) SOHC SEFI V10, 310hp @ 4250-rpm, 425 lb-ft @ 3,250 rpm 7.3L (444 cu.in.) V8 Turbo-diesel, 235hp @ 2600-rpm, 500 lb-ft @ 1,800 rpm