Originally Posted By: Linctex
Originally Posted By: Ducked
....they
probably catch-and-release some ferrous metals.
So now you've got
magnetised ferrous metals in your oil.
This is just an old wive's tale. I've seen nothing to prove this correct.
Well, since it's almost never discussed, you must know some old wives with pretty specialist interests.
I'd agree I've seen nothing to "prove this correct".
OTOH its intuitively VERY likely, and I've seen nothing to prove this incorrect either.
I've observed that ferrous particles on a (relatively weak) drain plug become magnetised. For capture-and-release to be "incorrect" the magnet has to have infinite capacity and be strong enough to retain all trapped material despite any turbulence or flow in the oil. I doubt these conditions are always met.
I've only seen one published (but un-referenced) mention of this point (apart from my posts, which maybe don't count) but if you know any other old wives who've gone public I'd be interested.
http://www.machinerylubrication.com/Read/781/particle-contamination
"Magnetic Susceptibility. Permanent magnets are used in some filters and online wear particle sensors. Particles of iron or steel that are attracted to a magnetic field are preferentially separated from the oil by these devices. Later, any particles that may have sloughed off these separators and sensors (due to shock or surge flow conditions) are often left magnetized. They can then magnetically grip onto steel orifices, glands and oilways restricting flow or simply interfering with machine part movement.
Additionally, directional control and servo valves commonly used in hydraulic systems deploy the use of electro magnets in their solenoids. The actuation of these valves can be adversely affected by the magnetic susceptibility of iron and steel particles that are attracted by the solenoid."
