Top clunker? The Ford Explorer

As Congress works to replenish the 'cash for clunkers' coffers, details on what drivers are trading -- and buying -- are emerging.

If you were wondering what America was going to do with all those Ford Explorers, wonder no longer. We're euthanizing them by the tens of thousands.

Of the top 10 vehicles traded in since the "cash for clunkers" program went live in late July, six are different model years of the once-ubiquitous Explorer, according to data collected by the Department of Transportation and reported by the Jalopnik automotive blog. Lumped together by nameplate rather than model years, its death-row companions include the big Ford F-150 and Chevrolet C1500 pickups, the Chevrolet Blazer SUV, the Jeep Cherokee and Grand Cherokee, plus the Dodge Caravan and Ford Windstar minivans.

The Explorer was for several years the nation's best-selling passenger vehicle, with more than 400,000 a year leaving showrooms in the late 1990s. The most-popular versions got around 15 miles per gallon.

As gas prices have risen and the fortunes of all SUVs dimmed, the Explorer fell on hard times, outsold in recent years by even the Toyota Prius. And now, the prospect of up to $4,500 toward a new car has led thousands of owners to dig out the keys to the family workhorse for one final ride. (See "'Cash for clunkers': The rules.")

Though all trade-in vehicles must be in drivable condition, dealers are required to disable the vehicles' engines before scrapping them, using a lethal injection of sodium silicate to replace the oil. The car is started and revved to at least 2,000 rpm until the engine stops, from three to seven minutes.

Gas savings about $1,100 a year

The analysis of the first 157,000 or so transactions under the Car Allowance Rebate System, or CARS, also revealed that the most-purchased new car was the Ford Focus, which gets an average of 28 mpg. The Transportation Department said the average mileage for cars to be scrapped under the program was 15.8; average mileage for their shiny replacements was 25.4 mpg.

For a car owner driving 15,000 miles a year and swapping vehicles achieving that fuel-economy average, the savings would be 384 gallons a year, about $1,150 at $3 a gallon.

Even just a week of cash for clunkers was enough to slow the dramatic, yearlong free fall in car sales. July was General Motors' best month so far this year, down just 19.4% over July 2008. Chrysler dropped only 9% -- a relief compared with declines of as much as 50% in recent months. Of course, its offer to match a clunker rebate with a $4,500 check of its own helped a lot.

Sales at Ford Motor, benefiting from an emphasis on its smaller cars and its Detroit rivals' bankruptcies, rose 2%.

"Cash for clunkers put us over the top," said George Pipas, Ford's chief sales analyst. "Lots of traffic, lots of sales."

As of Monday, $563.8 million worth of rebates had been processed through the government program, representing 133,767 new vehicles, the U.S. Department of Transportation said. A backlog of applications is expected to consume the balance of the $1 billion already set aside. Proposals to add an additional $2 billion to the program are working their way through Congress, enough to spur the purchase of about 500,000 more vehicles.

"This is the one stimulus program that seems to be working better than just about any other program. It's a lifeline for automobile workers and automobile makers," Transportation Secretary Ray LaHood told CNBC.