For diesel cars and light trucks.  Magnets are placed on fuel, air, and coolant units.

Increases fuel economy and/or horsepower (contingent largely on how one drives).  Fuel economy may improve by up to 20%-40%.

Increased heating capacity, lower fuel consumption and reduced emissions, less environmental pollution.

Improve combustion efficiency, air/fuel ratio, burns higher proportion of hydrocarbons in fuel.

EXAMPLES

United States Air Force

The USAF Management & Equipment Evaluation Program tested two vehicles over six months, one gasoline-powered and one diesel-powered. Because of the USAF’s fuel issuance methods, fuel consumption had to be measured indirectly by measuring unburned hydrocarbons in the vehicles’ emissions. The results, at a test load of 2500 rpm, were a reduction in unburned hydrocarbons of 75% (diesel) and 70% (gasoline). Carbon Monoxide emissions were also substantially reduced.
Beijing Railroad

A 16-valve diesel-engine locomotive that travels approximately 150,000 km a year was tested. For 6 months, data was collected on fuel consumption and carbon build-up with no magnets, and for another 6 months with magnets installed. Over the entire test, an average savings in fuel of between 4.5% and 4.9% was achieved with a maximum saving of 9.1% for one of the months. Simultaneously, hard carbon deposits changed to soft carbon resulting in significantly easier periodic maintenance.
Brazil EPA

Tests show 20.11% diesel fuel savings with substantial emissions opacity reduction.
India

Ministry of Surface Transport - Diesel Bus test resulted in a 16.8% diesel savings - 10.7 to 12.5 Kilometers per liter