Every time gasoline prices spike, con artists dust off products that claim to increase fuel economy significantly and entrepreneurs "invent" a few new ones. Their claims tout a 20- to 30-percent improvement, so, if you are getting 20 mpg, you will end up with 24 to 26 mpg. With the Internet, there is even greater proliferation in fuel-saving devices, or at least in the advertisement for them.
The simplest to use techniques are fuel additives. These should not be confused with fuel system and valve cleaners that usually do a good job in removing and preventing deposits and contaminants, but don't increase fuel economy by any measurable amount. Octane enhancers can increase power output of some engines, but again, not miles-per-gallons.
Some are magnetic devices attached to fuel lines that are supposed to alter the molecular structure of gasoline or align its molecules for more efficient combustion. Other devices installed in fuel lines contain metals that are supposed to ionize the fuel.
Compared to engines with carburetors, it is much harder to modify modern engines with electronic fuel injection and computerized engine management systems. Thus, some devices are designed for vehicles with carburetors, though a rapidly decreasing number. These include devices that bleed air into the carburetor or heat the fuel before it enters the carburetor. A popular technique induces air that is bubbled through a container of a mixture of water and anti-freeze before being injected into the carburetor.
For more modern engines there are devices that add a "mystery" liquid into the fuel/air intake system or into the combustion chamber. Others make some type of modification to the vehicle intake system or to the ignition system either as addition to the current one or as a replacement. More elaborate devices include a fan or turbine installed in the air-intake system to swirl the incoming air to improve combustion. Some inject air, water or other vapors or liquids into the fuel mixture before it enters the engine. Some add tiny amounts of platinum.
Seldom do you ever see claims backed up by results from laboratory testing, let alone testing by an independent or certified laboratory. Most use testimonies from "satisfied" users or endorsements from well-known people. In contrast, many recognized and basically unbiased sources like the AAA, Popular Science, Popular Mechanics, Consumers Reports and even the Mythbusters TV show have tested them, and found them marginally effective, at best. In some cases, when you order, you may not even get an actual device, just some instructions and drawings on how to build one yourself
Probably, the most comprehensive testing was done by Environmental Protection Agency for the Federal Trade Commission. The EPA evaluated over 100 gas-saving devices and did not find any product that significantly improved gasoline mileage. (See www.ftc.gov/bcp/edu/pubs/consumer/autos/aut10.shtm.)
While virtually all of the devices are useless, some can cause harm. They may increase emissions, meaning your car will no longer be able to pass a smog test. Others may require modifications considered to be illegal, like tampering with the smog control system. Also, they may upset the functioning of today's complex engine management systems resulting in, for example, triggering the CHECK ENGINE light. This could require a costly diagnosis of the OBD II system or smog test failure. Some additives may contain acetone or other alcohol-based materials that can dissolve plastic and rubber fuel system components.
The bottom line; don't waste your money on these unproven devices. If you are getting close to the EPA mileage ratings, they will not improve fuel economy. If you are getting much less, correcting the source of the problem is a better investment. This could be a tune-up, or just making sure tire inflation is proper.
It should be noted there are some techniques from very reputable companies that are usually aimed at increasing power and torque output that can also improve engine efficiency. These include high-performance air-intake and exhaust systems. However, these modification are expensive, costing $1,000 or more, and not for installation by most do-it-your-selfers.
Finally, conspiracy theorists say the automobile manufacturers and oil companies have suppressed all the fuel-saving devices that work. They say inventors have been bought off, threatened, or worse. Others say the automakers have devices that allow a car to get 100 mpg or run on water, hidden away. Ask you yourself, why would they be spending millions to meet more stringent CAFE requirements by increasing fuel economy by a few mpgs, when for a few dollars they could use one of these devices that claim to improve mileage by 20-percent, or more. Or if they worked, don't you think automakers, or even dealers, would be installing them on the gas guzzlers now languishing on their lots?
