Consumers went for miles-per-gallon in a big way in August, as U.S. light-vehicle sales achieved a record fuel-efficiency rating, the Ward’s Fuel-Economy Index shows.

The index, which measures the average miles-per-gallon per LV sold, hit a 23 mpg (10.2 L/100 km) average in the month, up 1% from the previous high set in July.

The August rating marked an 8% gain from year-ago’s 21.2 mpg (11.1 L/100 km) average.

The index is calculated using Environmental Protection Agency fuel-economy ratings for individual models and engine-installation rates gathered by Ward’s to estimate the relative fuel efficiency of U.S. car and light-truck sales on a monthly basis.

The Ward’s FEI indicates the “Cash for Clunkers” program, which offered consumers as much as $4,500 to trade low-mileage older vehicles for more fuel-efficient models during July and August, boosted the average fuel economy of LVs sold in both months to record highs that tracked well above trend.

The industry-wide index rating rose about 2% during the first half of the year, reaching 22.1 in June from 21.7 in January, before taking a nearly 3% jump from June to July (22.7).

The subsequent increase in August pushed the industry’s rating to 23 for the first time since October 2007, the baseline for the index

Related document: Ward's Fuel Economy Index

Eleven auto makers registered their highest scores to date on the Ward’s FEI in either July or August. The Detroit Three were among those setting records during those months, collectively posting their highest-ever rating of 20.4 in August, up more than 4% from year ago.

Even Asia-based companies, which regularly enjoy high fuel-efficiency ratings, saw a jump, combining for a record 25.1 in August.

American Honda Motor Co. Inc., Hyundai Motor America, Kia Motors America Inc., Mazda North America Operations, Nissan Motor Corp. and Toyota Motor Sales U.S.A. Inc. all achieved their highest ratings in either July or August.

Toyota finished atop the index in each of the last two months, setting an industry record in July with a rating of 26.9. The auto maker delivered 54,396 Camrys (including 2,114 hybrids), the second-best month since the car was introduced in February 1983.

Kia and Hyundai finished second and third on the Ward’s FEI in August, at 25.1 and 24.9, respectively.

Taken together, European auto makers also attained their highest ratings to date in July (22.1) and August (21.9), with Volkswagen of America Inc. (23.) and BMW AG (22) setting individual records in July.

An obvious effect of the Cash for Clunkers programs was to skew sales toward more fuel-efficient segments. In July and August, cross/utility vehicles for the first time outsold all other light-truck sectors combined.

The Ward’s Small Car category outsold the Middle Car group for two consecutive months, only the second time that’s happened since at least 1980.

But even within larger-vehicle groups, sales shifted toward more-efficient models, as Middle Cars, Large Cars, Vans and Pickups all achieved record index ratings in either July or August.

August’s FEI rating also was boosted by delivery of 34,331 hybrid cars and light trucks, the second-highest monthly volume ever. The average fuel economy for the 11 hybrids currently for sale in the U.S. range from a low of 28 mpg (8.4 L/100 km) for the Saturn VUE to 46 mpg (5.1 L/100 km) for the Prius.

As sales volumes decline, there likely will be a decided falloff in average fuel efficiency in September and throughout the fourth quarter, as the “payback” effect of Cash for Clunkers on LV sales will tend to affect the fuel-efficient segments that benefitted most from the government incentive program.

Nonetheless, with the calendar year tracking 3.5% above year-ago and more efficient ʼ10 models coming into the market, the Ward’s FEI rating for all of 2009 should finish well above 2008, despite the gas-price-induced move away from larger cars and light trucks last year.

jsousanis@wardsauto.com