Robert Mueller deals in chemicals for a living — things that can unstick glue, thin paint, make plastic — but he'd never seen an order like the one he got for sodium silicate.

The compound is typically used to repel bugs or seal concrete, but this buyer's online order form betrayed a whole different intent: "To Kill Car Engines."

"That worried me a little, so I picked up the phone and called the gentleman," recalls Mr. Mueller, an owner of chemical-firm CQ Concepts Inc. in suburban Chicago.

What Mr. Mueller discovered is that sodium silicate is the designated agent of death for cars surrendered under the federal cash-for-clunkers program. To receive government reimbursement, auto dealers who offer rebates on new cars in exchange for so-called clunkers must agree to "kill" the old models, using a method the government outlines in great detail in its 136-page manual for dealers: Drain the engine of oil and replace it with two quarts of a sodium-silicate solution.

"The heat of the operating engine then dehydrates the solution leaving solid sodium silicate distributed throughout the engine's oiled surfaces and moving parts," says the National Highway Traffic Safety Administration publication. "These solids quickly abrade the bearings causing the engine to seize while damaging the moving parts of the engine and coating all of the oil passages."

In a nation packed with experts on how to keep cars running, the engine-killing powers of sodium silicate are a well-kept secret. "I, like, have so not even ever heard of this before," said Robert Lutz, new marketing chief and renowned "car guy" at General Motors Co., in an email.

Often called liquid glass, sodium-silicate solution has been better known for being used to save motors rather than killing them: It is used to stop leaks in the gaskets that seal cylinder heads to engine blocks.

At dealerships across America, mechanics accustomed to fixing engines are battling for the chance to ruin them. "Everybody wants to go first, so I'm probably going to have to make them draw straws," says Jim Burton of Randy Curnow Buick Pontiac GMC in Kansas City, Kan. As service manager, however, he might reserve that thrill for himself. "I can't wait," he says.

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