Does anyone have an educated guess as to whether this magnet would significantly extend the life of an automobile engine? The Filter-Mag is a large, flexible magnet that wraps around an oil filter, and thereby allegedly traps steel particles that would otherwise harm your automobile’s engine.
I can understand the appeal, but the added benefit doesn’t seem worth the $50- $75.
Isn’t that what the filter does? Seems like you’d be better off just coughing up a few dollars for a better filter.
And what if it slips off, then suddenly all the accumulated particles go heading towards your engine all at once?
And if you have an aluminum engine? Its not going to pick aluminum particles.
No, that entails purchasing the “Super Miracle Magnet.” 
It’s not a new idea. You can buy an oil drain plug with a magnet on it for much less than these folks want. You can also get a strong magnet to stick on the transmission pan pretty cheaply.
The fact remains, though, if you have a significant amount of iron or steel shavings floating around in your engine, you have big trouble around the corner, and a magnet won’t help.
Some (all?) cars already have a magnet on the oil plug. It’s one of those things I think alot of people don’t realize they should be wiping off when they change thier own oil.
That won’t work all that well, if at all. Basically, your transmission case is going to act in a manner roughly analogous to a Faraday shield. The magnetic field is going to tend to mainly follow the path of least permitivity, which is through the steel of the transmission body. Unlike a Faraday shield, however, some of the magnetic field will still penetrate through to the other side, but it will be strongly attenuated.
Although I will bow to the knowledge of the actual mechanics who post here, this sounds about as useful as snake oil to me. A decent filter should already be stopping anything this magnet would hope to grab.
Metal in the engine would come from one of several sources
[ul]
[li] machining swarf [/li][li] material worn off of bearings[/li][li] material worn off crank and camshafts[/li][/ul]
If you have an aluminum engine most of the first item will be aluminum, a magnet won’t help much. Unless of course you buy an aluminum magnet. 
As far as the bearings go, much of that material is non ferrous and a magnet won’t help.
Material worn from the crank and cam is ferrous and will be picked up by a magnet.
As has been mentioned many drain plugs have magnets on them.
As far as the transmissions go, many if not most automatic transmissions come with a magnet inside the oil pan from the factory.
Save your money.
I just dropped in to say thank you for introducing me to this totally unexpected and delightful word. I’ve now added “machining swarf” to my List of Weirdly Euphonious Phrases That I Just Like To Say Without Really Caring What They Mean, such as:
I’m afraid that’s not correct. Transmission cases are cast aluminum. Virtually every car manufacturer puts magnets in the steel pan at the factory. Those magnets always have a clump of powder-fine debris (from steel internal parts) clinging to them.
In that case, a magnet isn’t going to stick to them, now will it? Unless you glue it on.
It doesn’t take 50+ bucks worth of magnet to attract the fine ferrous debris that might be in an engine. The magnets in some drain plugs probably retail for 1 or 2 bucks. But if there were truly a need for a filter magnet, the car manufacturers would use them. They don’t because a good quality filter is sufficient. Many different engines (some Toyota and Volvo designs come to mind) routinely go several hundreds of thousands of miles with reasonable care.
Just make sure you use genuine transmission case glue.