To test the claims of a fuel-saving device, the EPA has the voluntary Aftermarket Retrofit Device Evaluation Program. Manufacturers willingly submit their fuel-saving device to the EPA for testing. The EPA then uses the device according to the manufacturer's directions in controlled settings and reports on its findings. According to the EPA, "The purpose of the Aftermarket Retrofit Device Evaluation Program (also known as the '511 Program') is to generate, analyze, and disseminate technical data on the effectiveness of such products."
Here's the catch: Since the testing program is voluntary, according to the EPA, very few fuel-saving device manufacturers actually use it. In fact, on the EPA's Web site that lists the test results, only 93 fuel-saving products have undergone testing since 1970.
As the EPA says, "EPA does not approve, certify, endorse, or register any products that pass through this voluntary evaluation program. Neither does EPA approve, certify, endorse, or register any independent laboratory or the test results from any independent laboratory. Any claims by a manufacturer to the contrary are false."
In many cases, the devices or additives tested by the EPA not only didn't improve fuel economy, but many actually made fuel economy worse or damaged the car. Other organizations that have tested some of these fuel-saving devices offered over the years, like Popular Mechanics magazine, have come to similar conclusions. In some cases, the EPA warns, installing the devices could constitute tampering with your car's emissions system, which not only increases pollution, but will also void your warranty and could make you subject to legal penalties. ("Freeze! It's the emissions police!")