Fuel saving devices

Since the development of the internal combustion engine, people have looked for ways to increase its efficiency, in order to increase the fuel economy of the automobile.

Although many technologies have had a beneficial effect on vehicles' fuel economies, claims as to the efficacy of some devices have clearly been bogus or misleading.

An early example of a "fuel saving gadget" sold with claims that were difficult to justify is the 200 mpg carburettor designed by Canadian inventor Charles Nelson Pogue

A good thing to keep in mind when examining fuel saving devices is that most of these claim major increases in combustion efficiency, something that sounds attractive when you consider the average gasoline engine rarely exceeds 35% efficiency. However, the weak point of the engine is not converting the fuel into heat, but the heat into mechanical energy, hence the reason why many fuel saving devices don't work as claimed. On modern engines there is relatively little scope for improving combustion efficiency. Most of what can be legitimately achieved is done by reducing parasitic losses of accessories e.g. fans, water pump, and pumping losses by taller vehicle gearing.

One reason that ineffective fuel saving gadgets have had some success in the marketplace is that it is surprisingly difficult to measure the fuel economy of a vehicle. This is because of the high level of variance in the fuel economy of a vehicle under normal driving conditions. Consequently, it is extremely difficult to measure small changes to fuel economy.

The large degree of fuel economy variance means that due to psychological factors of selective perception, consumers can be mislead as to the effectiveness of a device.

For this reason, regulatory bodies have developed standardised drive cycles that are useful for statistically significant comparisons of fuel economy


Vehicle Design Technologies

It is both easier and far more cost effective to design a vehicle to be fuel efficient than to modify an existing vehicle to improve its fuel economy.

Some effective technologies that can improve the fuel economy of a internal combustion engine vehicle include Fuel injection, Continuously variable transmission, Electrical motor assistance (known as hybrid vehicles), variable displacement, technologies to reduce vehicle weight, various friction reducing measures, and vehicle shell designs that reduce aerodynamic resistance (this doesn't improve engine efficiency, but reduces engine power needed to overcome drag, and consequently fuel consumption).

A more comprehensive list can be found in the category Engine technology


Retrofit devices

There are many devices currently being sold as "fuel saving devices" that have negligible or even harmful effects on fuel economy. The US environmental protection agency has issued reports on a number of aftermarket devices that claim to improve fuel economy

Some of these devices include:


Fuel additives

Materials which are added to the fuel include tin, magnesium and platinum compounds. The claimed purpose of these devices is generally to improve the energy density of the fuel by virtue of the materials added. Acetone is another additive, but may dissolve plastic parts in the fuel system.

These should not be confused with fuel system and valve cleaner additives which remove contaminants from the fuel system and/or remove deposits on intake valves.

Magnets attached to fuel lines have been claimed to improve fuel economy by aligning fuel molecules.


Vapour transfer devices

Various devices claim to improve fuel efficiency by changing the way that liquid fuel converts to fuel vapour. These include "Swirlers" to increase turbulence in the intake manifold and heaters



Friction reducing measures

Reducing friction is undoubtedly a powerful tool in reducing fuel consumption. Hardened silica tyres have lower rolling resistance than standard rubber tyres.

The typical lubricating oil used in engines has decreased in viscosity over the years. However, using a lubricant with lower viscosity than the lubricant specified by a vehicle manufacturer may damage an engine.