As Seen On The Internet:
A few filter manufacturers are extolling the virtue of placing magnets in the filters to trap metal particles. They claim that magnetic forces stabilize the
oil molecules; that the longer the magnetic field is in place the greater the benefit; that fuel mileage is increased;
oil consumption and emissions are decreased; and engine power is increased. None of these claims are true and several are impossible.
Magnets do remove some sub-micron sized iron particles that are there as catalysts to aid combustion and also attract small ferrous metal particles that might be inside the engine
oil galleries, but neither of these account for much effect in the real world. The bulk of the metallic particles floating around in an engine are from bearing materials and these aren't ferrous. Magnets won't "see" them.