An early example of such a device sold with difficult-to-justify claims is the 200 mpg‑US (1.2 L/100 km) carburetor designed by Canadian inventor Charles Nelson Pogue.
[2] Other organizations generally considered reputable, such as the American Automobile Association and Consumer Reports have performed studies with the same result.
[3][4] One reason that ineffective fuel-saving gadgets are popular is the difficulty of accurately measuring small changes in the fuel economy of a vehicle.
For these reasons, regulatory bodies have developed standardized drive cycles for consistent, accurate testing of vehicle fuel consumption.
[5] Where fuel economy does improve after the fitment of a device, it is usually due to the tune-up procedure that is conducted as part of the installation.
Such alterations to the drive systems for alternators or air conditioning compressors (rather than the power steering pump, for example) can be detrimental to vehicle usability (e.g., by not keeping the battery fully charged), but will not impair safety.
[20] The maker disputed claims that the device has no effect,[21] and proposed changes to the Consumer Reports testing procedure, which when implemented made no difference to the results.
A similar claim of 300 mpg‑US (0.78 L/100 km) for any vehicle would require an engine (in this particular case) that is 300% efficient, which violates the first law of thermodynamics.
This fiction is thought to have started after Canadian Charles Nelson Pogue filed patents in the 1930s for such a device.
[27][28][29] The popular U.S. television show MythBusters investigated several fuel-saving devices using gasoline- and diesel-powered fuel-injected cars under controlled circumstances.
The show also tested a carburetor that, according to its manufacturer, could improve fuel efficiency to 300 miles per US gallon (0.78 L/100 km).
The show also noted that if any of the devices they tested actually worked to the extent they were supposed to, the episode would have been one of the most legendary hours of television.