ACCUMULATION OF SMALL ADVANTAGES.  In small quantities, antifreeze is relatively cheap, and at low fuel prices, the additional wind resistance offered by radiators is no big deal.  Thus, motor vehicles, until recently, did not have radiator shutters.  (Diesel locomotives, which have high-volume cooling systems for which antifreeze becomes uneconomic, have long had radiator shutters, with temperature-controlled automatic shutters being offered as early as the 1950s.)

Rising fuel prices, and competition to offer better fuel economy without turning all automobiles into golf carts, make the automatic shutter in the grille something worth developing.
[Ford vehicle engineering chief Don] Ufford said the shutters notion had been studied for years but was not practical until breakthroughs in engine computers.

Now the shutters could be opened or closed based not just on engine temperature, but outside air temperature, vehicle speed, air-conditioning demand and other factors.
Under constraints that previously didn't bind, or that didn't have a high shadow price to violate, such improvements probably weren't cost-effective.
The goal with the Cruze Eco was to create a car with the gas mileage of a gas-electric hybrid, but without the higher price tag that comes with the hybrid's expensive batteries and electric motors.

Using shutters allowed GM engineers to come up with a car that can handle the worst-case scenario for engine overheating — pulling a trailer up a Death Valley mountainside on a summer day — yet pick up the benefits of less wind drag by shutting the louvers when days or nights are mild.

Makes sense, says Robert Sawyer, a professor emeritus in engineering at the University of California-Berkeley. He says that in order to meet the tougher government gas-mileage regulations, automakers "will need everything they've got" to pick up an extra mpg or two. "Anything that is simple," is sure to be part of the formula.
Simple, however, is determined relative to a cost-benefit calculation.

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