Having Magnets actually works. Tried it before and still doing it.
Anyway, putting a solid heavy cylinderical magnet into an oil filter has its advantages:
Firstly,Magnets actually helps remove 40times more grit than the filter alone.(longer oil and filter service life)
Secondly, it also reduces toxic tailpipe pollution by at least 15-20%(less pollution)
Thirdly, 3% to 5% increase in fuel economy(better gas mileage)
Fourthly, at least 5-15times reduction in engine wear(Engine lasts longer)
If magnet is placed outside the oil filter, it doesnt attract as much grit(but better than nothing, right?)
So for those who wants to save fuel costs, save the environment, and not worry about the engine, put a magnet. But remember when putting a magnet into an oil filter, use a heavy solid magnet.
ps.Information on the four advantages taken from track mechanics and service shops.