We are still receiving reports of new devices comprising magnets that claim to improve fuel economy and/or reduce exhaust emissions, when fitted to the fuel line of a car. They may be referred to as filters, catalysts or the like, working on the principle that a special magnetic field applied to the fuel can improve combustion.
In view of our past experience with this type of product, we are not recommending their purchase by members of the Automobile Association until we have convincing independent evidence of their effectiveness. The main reasons for this are as follows:
1. There is no demonstrable effect due to these relatively small magnetic fields on hydrocarbon liquids such as petrol or diesel fuel. A magnet cannot provide oxygen and neither can it change the amount of heat released from burning the fuel.
2. Liquids cannot "retain" any magnetic effect when they leave the magnet, even if affected when within it. Hence you cannot charge a liquid in the way that a dust particle can be charged.
3. There is no evidence that combustion is improved, and we have not seen authoritative independent test results to confirm the claims made regarding fuel consumption, power output or emissions reduction.
4. Particular care has to be taken in the case of tests carried out using the normal garage "MoT" type emissions test equipment. These tests are designed to detect a defective engine, and do not measure the on-load exhaust emissions of a vehicle. It is totally misleading to interpret a change shown by this equipment after fitting a device as evidence of improved combustion.
5. A modern car engine will typically fail to completely burn something like half of one percent of the fuel it uses. This therefore will be the sort of improvement that could be expected by a device that ensured complete combustion of all the fuel - not 8-10% as may be claimed.
6. There are very closely controlled tests of exhaust emissions and fuel consumption that are used by the industry to detect the very small changes that are critical in designing an engine to meet current legislation. These tests can be carried out by specialist laboratories and are the only reliable indication of an engine's emissions performance.
7. It is very difficult to assess the affect of an economy device on the operation of a vehicle in use on the road, particularly if the benefit is claimed to arise over a period. Hence road tests or user commendations need to be treated with a great deal of caution.
See also TIC03- Fuel Enhancement Devices Based on the Effects of Tin.
TIC04 10/98 This information has been prepared for the exclusive use of members of the Automobile Association. Automobile Association 1998