miniimage1 Be careful what you wish for. 

Just a week after launching the cash-for-clunkers rebate program, policymakers and auto executives are left sorting through the chaos caused by the program’s runaway success.

As of Friday, there was no knowing how much longer funding for the program will last. The Obama administration has reassured car shoppers and dealers that any trade-ins over the weekend will be honored at rebates for up to $4,500. Meanwhile, the U.S. House rushed to triple funding  for the program, adding another $2 billion in a bill that heads to the Senate where it could face tougher scrutiny.U.S. car sales for July, set to be released on Monday, are expected to show a turbocharged boost from the government program, a sleeper success in a string of policy steps aimed at stabilizing the U.S. auto industry that has included government-sponsored bankruptcies at GM and Chrysler.Before the rush of clunker trade-ins, analysts had been looking for industry-wide July auto sales to top 10 million units, the highest rate of 2009 and an encouraging sign the market has turned the corner. Investors have discounted some of that recovery. Shares in AutoNation, the No. 1 dealership group, have gained 48 percent since the start of the second quarter. Shares in the No. 2 dealership group, Penske Automotive Group, have more than doubled.With inventories tight, automakers also stand to gain as production — and revenues — increase in the second half. July sales data will help sort the winners from the losers, but the early anecdotal evidence suggests that the some of the biggest gains have gone to the automakers that were already outperforming. Hyundai says about 18 percent of its sales in the month of July included a cash-for-clunker backed trade-in. Ford,  which is seeking to distance itself from the rest of Detroit, reports that cash-for-clunker trade-ins were boosting sales of smaller, more fuel-efficient cars as opposed to crossovers and trucks. That is also the area where Ford’s product line-up is seen as giving it an edge against GM and Chrysler.