Here's a copy of a post in the oil filter selection about magnet performance based on it location, the sump or the filter.... Our thoughts that placing the magnet on the filter would be a problem because of the flow rate past the magnet and it turned out that it might be more important to have more oil flow past the magnet and to let the magnet do it's work.
If you put a magnet near the drain plug how do you clean the fuzzy stuff off?
On 2 delivery vans we put a magnet on the oil pan of one van and on the oil filter of another. Both vans are driven on exactly the same route and the same 5 drivers drive either van, day in and day out. We looked at the deposits inside the oil pan with a flexible fiber optic viewer and cut the oil filters open for viewing. The oil filters always collected more fuzz than the oil pan. Now all the deliver vehicles get magnets on the oil filters.
