US polices add-ons that claim to cut gas mileage

How can you tell whether adding a particular device to your car will actually increase its mileage per gallon? By reading test reports, of course -- but only very carefully selected ones. The only tests with validity, in the eyes of the Federal Trade Commission, are those run by the Environmental Protection Agency (EPA).

The EPA is the federal office charged by Congress to sort out valid add-ons from the fizzles and the fakes. So far, its test work has not been encouraging.

Aware of about 100 devices claimed to save gas, the agency has already tested more than 40, selecting at least one from nine major categories. The number of fizzles has been impressive.

Not until last August did the EPA finally report a device that actually save gas. it was a switch that automatically shut off the carhs air conditioner when the car engine was accelerating or laboring. (Of course, the switch is effective onl if the air conditioner was turned on in the first place.)

The nine categories into which the agency sorts the so-far-unsuccessful add-ons are air bleeds (adding air to the air-fuel mixture after carburetion); vapor air bleeds (similar, but pulling the air through a vater mixture first); crburetor/intake-manifold junciton devices; intake system modifications; fuel-pressure regulators; gasoline additives; exhaust-gas-recirculation devices; ignition controls; and lubricants.

(Copies of the EPA test results may be obtained by writing to the Environmental Protection Agency, 2565 Plymout Road, Ann Arbor, Mich. 48105.)

While the EPA test is t he only one the Federal Trade Commission accepts as valid for advertising purposes, fuel-saving devices -- even those in the nine categories -- still untested by the EPA are not automatically consigned to villainy.

The EPA doesn't have to do all the testing. The Trade Commission will accept results from independent labs that use EPA procedures. And some mileage stretchers have already won good reputations for sound engineering.

Super-slippery mtor oil is one. It's been established that engine oil that has been modified to reduce friction or with lower viscosity can save fuel.

But questions of engine durability in early testing have delayed the oil's acceptance in Detroit.

Many add-ons can be trusted because they were later incorporated in production cars. Fan clutches, electrically driven (rather than belt-driven) fans, radial tires, electronic ignition systems, electronically controlled fuel-injection systems -- all were available as after-sale add-ons before incorporation in new models. They're still available for improving the mileage of older cars.

Some fuel stretchers have been proved in racing. Many devices that improve low-speed engine performance also improve fuel economy, usually at the cost of open-throttle performance.

The cost of such items -- carburetors, manifolds, camshafts, and the like -- must be considered in fuel savings, however.

Each auto company has an office that welcomes fuel-saver inventors. Of course, the car companies feel that fueleconomy improvement is a matter of tiny incremental improvements, and that their people are probably best equipped to find those improvements -- but they're taking no chances. They welcome inventors.

So faR, the earthshaking improvements in gas mileage simply haven't happened. Until a gadget comes along that works, and the EPA confirms that fact, motorists will have to stick to the old, well-proven methods.