How do you destroy an engine? Well, if you're the U.S. government, you use sodium silicate.
As you're no doubt aware, the U.S. has passed a "cash for clunkers" law that will give rebates to people who trade in old, thirsty vehicles and buy new, fuel-efficient ones. Since the whole idea is to get these old cars out of circulation, the program includes recycling them. But if someone takes that old engine out of the car and continues to use it, the whole point of the program is lost.
According to the website Cash For Clunkers, car dealers taking in these old vehicles will have to give each car a "lethal injection" in order to render it permanently inoperable. It seems that NHTSA wrestled with several options -- after a bit of whining in its final ruling that Congress never gave a definition of an "engine block" (follow that link to page 38) -- including parting out the engine components, destroying the oil filter threads, drilling a hole in the block, and running the engine without oil.
Finally, it determined that car dealers must do the equivalent of an oil change, but after draining the block, they add two quarts of sodium silicate, at a cost of about $7.00, and run the engine until the stuff dries up inside.
The stuff you learn on the Internet. Perhaps, as the website suggests, we should be buying shares in sodium silicate companies: it sounds like it's about to take off.