I see no proof that using magnets to condition diesel fuel works as a biocide
or performs any other useful function, yet people buy these and swear by them.
Does anyone know whether there has been any repeatable controlled experiment by
a neutral party which shows any benefits at all for running your fuel through a
powerful magnetic field before burning it? Sure, it might trap ferrous metal
particles suspended in fuel, but they shouldnt make it past your filters
anyway.

See:http://www.dieselcraft.com, the latest entrant into the magnetic fuel
conditioner industry. Until I see PROOF of efficacy, not suggestions or
anecdotal stuff I am sticking with Biobor biocide fuel additive and leaving
magnets for compasses and loudspeakers.