The Wastegate

February 2009 Column

Fuel is back down to somewhat reasonable prices.

Finally, you can afford to drive a DPF-equipped diesel truck.

What bothers me most about this green movement against black smoke is the stupidity behind the justification for the diesel particulate filter. We've just gone through a major energy crisis the likes of which this country hasn't experienced for 30 years. Prices for diesel fuel more than doubled over last summer, and while most us felt the pinch that put on a paycheck, it was salt to the wound to realize that you were burning more fuel than necessary to satisfy an EPA emissions mandate.

Want to play with some numbers? The GM Duramax LMM, Dodge 6.7L Cummins and Ford 6.4L Power Stroke DPF-equipped engines have been out on the market long enough for us to determine just what kind of an impact the DPF is really having on the trucks. You have to do a little math, but it's worth it to see what kind of cash you're throwing out the window.

We've tested several "off-road" modified versions of these trucks that have had the DPF removed. We've monitored fuel economy prior to and after the DPF was removed. On average, any one of these engines would see a 3.5 mpg improvement in fuel economy without the DPF (makes sense, since most any 2006 model year diesel pickup was getting around 14-15 mpg). And, the average baseline for these trucks with the DPF in place was 11 mpg.

Right off the bat, that's a 25 percent difference in fuel economy. But what do those numbers really mean?

On 30 gallons of fuel, you can travel 330 miles with the DPF and 435 miles without it. Throw in an average price-per-gallon of diesel fuel over last summer of $4.00 and look at the numbers.

You can drive 330 miles on $120 worth of fuel with the DPF. You can drive 105 miles farther on the same $120 worth of fuel without the DPF.

Need more math?

With the DPF, that same truck cost its owner 36.3 cents per mile to operate.

Without the DPF, that same truck could operate at 27.5 cents per mile. Say the average daily-driven diesel truck logs 30,000 miles over the year. At a 27.5-cent-per-mile operating cost, you'd be out $8,250 for the year's worth of fuel operating that truck without a DPF. Compare that to the $10,890 it would cost you cost to put the same amount of miles on a DPF-equipped truck. That's an additional $2,640 to do the exact same job in a truck that has nothing different on it aside from a canister filled with ceramic tubes. We call that the dirty tax.

But that's just the cash we're talking about. This is all about going green, right? Well, 30,000 miles at 14.5 miles per gallon (no DPF) would take 2,069 gallons of diesel fuel. Throw the DPF under the same truck and you would burn-get this-2,727 gallons of fuel. That's 658 more gallons of fuel used, burned, consumed (or wasted).

Let's also say, for example, that between Ford, Dodge and GM, 300,000 DPF-equipped light-duty diesel pickups were sold between May 2007 and May 2008. If each of those trucks is consuming more 658 gallons of extra fuel, it would mean that we've consumed 197.4 million more gallons of fuel than would have been used by the same number of non-DPF diesel pickups in one year.

All in the name of what, lower particulate emissions? (Remember, the DPF is nothing more than a soot trap.)

But hey, look at the bright side. This just might get us off of foreign oil sooner than anyone imagined.

At this increased rate, we'll have it all used up in no time.


Email Ryan at



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