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Truck Trend Garage: Decreasing Fuel Economy

Alex Steele
Feb 4, 2010
Photographers: Steve Austin
Q: In "Truck Trend Garage" (November/December 2009), a reader asks about the decreasing fuel mileage of his Chevrolet truck. The authors forgot to mention one simple issue that could be the root cause of the reader's problem: ethanol. If the laws changed in the reader's area, the fueling station changed policy, the reader changed gas stations, etc. a 10-percent ethanol blend that is catching on in many states will cause the same fuel economy decrease that is perplexing the reader. I've been calculating the fuel consumption loss due to the ethanol additive for many years and it varies between 10 and 15 percent depending upon the vehicle, for the legal "dose" of 90 gasoline/10 ethanol blend prevalent in many states. In addition, because ethanol sells for less than gasoline, there is an inherent incentive to add this to gasoline at the distributor level and increase profit margins. It is nearly impossible to detect the presence of this small percentage of the product unless you possess an ethanol test kit.
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A: You may have a point. The 10-percent ethanol blend now being pumped in all 50 states could've affected that reader's drop in fuel economy. But that would only be the case if he switched fuels when the problem began, and I still wouldn't believe E10 to be the root cause. The studies I've seen show about a three percent drop in mpg when comparing straight gas with E10. The U.S. Department of Energy stated in "Biofuels & Greenhouse Gas Emissions: Myths Versus Facts," dated April 18, 2008, that "while ethanol delivers less energy than gasoline on a gallon-for-gallon basis, today's vehicles are designed to run on gasoline blended with small amounts of ethanol (10 percent or less) with no perceptible effect on fuel economy." Our reader, going by his numbers, lost an average of about eight percent in fuel economy. He was also experiencing a misfire condition and may have had the original oxygen sensors in a high-mileage Chevy truck. I don't know about you, but when someone tells me his engine is losing a cylinder and mpg went down, I would be more concerned about the misfire. Ethanol does have a lower energy content than gasoline, but the octane rating is actually higher, which enables it to produce more power--even more so when assisted by high compression and/or forced induction. I, personally, am an ethanol hater. Not due to fuel economy or price (E10 usually costs less), but because of the alcohol-based corrosion it produces in fuel systems. It doesn't seem to affect daily driven vehicles at this point, but park a carbureted motorcycle or classic car/truck for a few months. Next time you fire it up it may not start, due to obstructed fuel jets.
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How To Reach Alex
If you have a technical question regarding your pickup, SUV, or van, feel free to contact Alex, a master technician with the National Institute for Automotive Service Excellence. Send a letter to him in care of Truck Trend Garage, 831 S. Douglas Street, El Segundo, CA 90245, or e-mail us at Please include the VIN with your question. Due to the volume of questions received every month, we cannot guarantee that everyone's question will be personally answered or will appear in the magazine.

Can't wait for help with a problem you're having with your Truck or SUV? Ask the expert we trust here at Truck Trend Garage—visit Alex Steele at

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