How effective and useful can a magnetic plug be when many of today's engines use alloy aluminium for heads, engine blocks, pistons, etc. In many engines only the piston pins, piston rods and crank shaft use ferrous metals, none of which, hopefully, should be contributing significant particles for this plug to pick up. In the iron block and head era this had an application and I've owned cars that had them. Is this an idea whose time has passed, kind of like promoting your "Buggy Whip Factory" after cars have put all the horses out to pasture?
most all blocks use some sort of iron liner. camshafts, followers, valves, oil pump, gears, timing chains, rockers, etc are all normally made out of some sort of iron or steel.
i know that there are titanium valves and springs, aluminum rockers, some engine dont even have rockers.
but my point is that there are still alot of magnetic parts to an engine. a magnetic drain plug is still probably very usefull for an engine.
they certainly work wonders on a transmission weither its an auto or manual. they work pretty good on rear ends as well.
Chrome, used to plate piston rings, is also a very magnetic metal. (Chromium dioxide was used for years in high-end audio recording tape as well as video tape.) Chrome is even harder than iron and steel alloys, thus potentially more abrasive as particulates, than iron. Cobalt may be alloyed in certain engine component metals. It's also very magnetic. (Cobalt "doped" ferrous oxide magnetic recording tape has also been used for years to mimic the magnetic performance of chromium dioxide magnetic recording tape.) Going to aluminum blocks and cylinder heads by no means substantially reduced, let alone elliminated, the amount of magnetic wear metals present in most production aluminum engines. (The major exception being engines cast from high silicon content aluminum in which the pistons and rings are in direct contact with a smooth, hard, silicon bore surface after acid-etching the machined cylinders. The not-quite-ready-for-prime-time Chevy Vega motor that pooped anytime after 40,000 miles was a prime example. GM and others finally tamed the technology.)