1: Fuel Catalysts
These devices insert pieces of various metals into the fuel. The claim behind them is that the metals produce a catalytic reaction in the fuel, removing impurities and making it a more efficient energy carrier. Some of these devices even claim to remove harmful bacteria from the fuel.
The merits of these devices are hard to measure without the aid of a mass spectrometer or other equipment that can measure the chemical changes that might take place in the fuel. But this could all be a moot point, given another factor: Modern engines are optimized to run on modern fuel in its current state. Changing that state moves the fuel away from the optimal fuel the engine is designed to burn. This may only be a minimal change, but it still strays from the standard engineered into the engine and its control systems. If the catalyzed fuel does indeed have properties that make it burn cleaner or faster, the engine's controls may not be able to adapt in a way that realizes any mileage improvements [source: Tony's Guide to Fuel Saving Gadgets].
2: Fuel and Oil Additives
The auto parts stores are full of them: racks of cans, bottles and cartons containing additives that claim to enhance power, reduce wear and improve engine performance -- and all you have to do is pour them into the oil pan or fuel tank. Thanks to their relatively low cost, these are some of the most often-seen mileage-enhancement devices. But not all of them work as advertised.
Modern car and truck engines are the result of decades -- even centuries -- of refinement. Parts do wear out, and any device that turns a series of small explosions into propulsion is bound to wear down over time. But vehicle engineers test engines for tens of thousands of hours, often under conditions worse than a road-going car would ever encounter, and design their products accordingly. As a result, even fuel and oil additives that work as claimed may only show minimal benefits when used.
Some oil additives, for example, are advertised with a striking commercial: an engine is run with the additive in it, and is then drained of oil and restarted. Miraculously, the oil-less engine runs. What the advertisement doesn't say is that the engine, like many modern engines, is likely sturdy enough that it can run temporarily with no oil in the pan. The running engine is less a tribute to the oil additive than to the engineers who designed its tight tolerances and high-wear materials [source: Tony's Guide to Fuel Saving Gadgets].
Some additives may indeed work. But understanding which ones can make a difference for your car or truck requires a thorough understanding of both the engine and the additive.
3: Fuel Vapor Injectors
Gasoline's ability to burn changes along with its physical state: In liquid form, it burns too slowly to be useful for combustion. But when vaporized, gasoline burns at the explosive rate needed to power an internal combustion engine. Hucksters have been leveraging this fact for years.
One of the more common gadget hoaxes on the market is the fuel vapor injector. Allegedly, this device converts the fuel into a fine vapor before it reaches the engine, which supposedly lets the fuel burn more efficiently.
The problem with these devices comes not at the point of ignition, but at the tail end of the modern car or truck. An exhaust sensor measures the amount of oxygen in the vehicle's exhaust, which can indicate whether the engine is taking in the correct fuel-to-air mixture. Adding extra vaporized fuel through a vapor injector can cause the engine to run rich, with too much fuel and not enough air. The engine's computer would then adjust its fuel injectors to achieve the proper fuel-to-air ratio. At best, this means the engine would run exactly the same as it did without the vapor injector. At worst, a poorly installed vapor injector could cause part of the cylinder bank to run rich, sapping engine performance as the computer makes additional adjustments to address the imbalance [source: Allen].
4: Engine Ionization
These devices, which often attach to spark plug wires or the car's distributor, supposedly improve fuel burn by creating an "ionic corona" around the engine. Supposedly, this performs the same function as fuel ionizers, just closer to the point of ignition.
As mentioned before, the supposed molecular breakdown caused by ionic forces can't really happen. The molecular separation the ionizer claims to produce is what happens during combustion, and gasoline in its unburned form is a poor conductor. It stands to reason that, if gasoline were volatile enough to break down when exposed to a small electrical field carried by a bolt-on ionizer, the much larger field generated by the spark plugs, alternator and distributor would cause the same breakdown well before the gasoline reached the engine [source:Herning].
This is possibly one of the worst hoaxes thrown at drivers. In tests, ionizing devices revealed themselves to be little more than bundles of cleverly packaged wire, which could cause short circuits or fire hazards if attached to the wrong parts of a car's engine [source: Allen]. This is definitely one hoax to avoid at all costs.
5: Fuel-line Magnets
These devices, like fuel ionization systems, allegedly prepare the fuel to burn better when it reaches the combustion chamber. Rather than using electric fields to do the job, however, fuel-line magnets claim to use powerful magnetic fields to break down fuel into its basic components.
As is the case with fuel ionizers, fuel-line magnets serve little purpose other than to separate uninformed drivers from their money. Petroleum fuels are ubiquitous because of their stability -- although they can't pack the same punch as fuel sources like hydrogen, they're much safer and easier to handle. Petroleum fuels, in fact, are too stable to be significantly altered by something as small and simple as a magnet placed on a fuel line. Even if a magnet could produce a significant electrical field, that field would be altered by the metal of the fuel line, tank and components. If anything, an extremely strong magnet might disrupt some of the car's more sensitive electronics, although even this is unlikely, given the careful engineering that has gone into today's reliable electronic components [source: Allen]
