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Gearbox Magnetic Drain Plug Magnet Strength Mon Jan 12, 2009 1:43 am
K-BIKE
Life time member
Hi Folks,
I drained my gearbox oil a week or so before Christmas and looking at the magnetic drainplug was congratulating myself on how little metal had accumulated given a couple of hamfisted or should it be hamfisted and hamfooted clunky changes that I had made.
When I cleaned the plug I casually tried with a screwdriver to test how strong the magnet was and with great consternation noted it was barely magnetic! To say I was amazed was an understatement so I decided to refill the gearbox with oil and then order a new drain plug from BMW to compare its strength with the old one.
That plug duly arrived just before Christmas and it was a much stronger magnet and over the Christmas break I decided to drain the gearbox again fit the new one and during that process compare the strength/appearance of the magnets.
First off the new drainplug magnet will jump up off the table and stick to a screwdriver held a few millimetres above it whereas the old one wont and can only just be persuaded to stick to a very carefully held screwdriver touched onto the plug and raised very gently, any wobble drops it off immediately. Physically the visible difference was the diameter of the magnets, the old weak one has a much larger diameter magnet than the stronger new one.
As a by the by one characteristic of magnets is they possess a physical characteristic called the Curie point which is the temperature at which ferromagnetic materials spontaneously lose their magnetism. The Curie point of many magnets is quite high but for the class of super magnets one can buy easily specifically NdFeB (Neodymium Iron Boron) or Neo magnets it is surprisingly low at 80 degrees C for the standard version although higher temperature grades are available. The implications of that is if one were to put a Neo magnet in a sump of say an auto transmission or gearbox to suck out any metallic particles one would have to hope the oil will never get to a temperature greater than 80C since if it does the beard of particles stuck to the magnet will break free - not good at all. I do know the magnets in the BMW drain plugs are not Neo thank goodness, what their Curie point is I don't yet know.
I guess the important issue for all of us to check the magnetic strength of our drain plugs when we drain the oil next since if they are like my old one they are possibly not grabbing all particles whizzing by in the threshing oil.
Regards,
K-BIKE
I drained my gearbox oil a week or so before Christmas and looking at the magnetic drainplug was congratulating myself on how little metal had accumulated given a couple of hamfisted or should it be hamfisted and hamfooted clunky changes that I had made.
When I cleaned the plug I casually tried with a screwdriver to test how strong the magnet was and with great consternation noted it was barely magnetic! To say I was amazed was an understatement so I decided to refill the gearbox with oil and then order a new drain plug from BMW to compare its strength with the old one.
That plug duly arrived just before Christmas and it was a much stronger magnet and over the Christmas break I decided to drain the gearbox again fit the new one and during that process compare the strength/appearance of the magnets.
First off the new drainplug magnet will jump up off the table and stick to a screwdriver held a few millimetres above it whereas the old one wont and can only just be persuaded to stick to a very carefully held screwdriver touched onto the plug and raised very gently, any wobble drops it off immediately. Physically the visible difference was the diameter of the magnets, the old weak one has a much larger diameter magnet than the stronger new one.
As a by the by one characteristic of magnets is they possess a physical characteristic called the Curie point which is the temperature at which ferromagnetic materials spontaneously lose their magnetism. The Curie point of many magnets is quite high but for the class of super magnets one can buy easily specifically NdFeB (Neodymium Iron Boron) or Neo magnets it is surprisingly low at 80 degrees C for the standard version although higher temperature grades are available. The implications of that is if one were to put a Neo magnet in a sump of say an auto transmission or gearbox to suck out any metallic particles one would have to hope the oil will never get to a temperature greater than 80C since if it does the beard of particles stuck to the magnet will break free - not good at all. I do know the magnets in the BMW drain plugs are not Neo thank goodness, what their Curie point is I don't yet know.
I guess the important issue for all of us to check the magnetic strength of our drain plugs when we drain the oil next since if they are like my old one they are possibly not grabbing all particles whizzing by in the threshing oil.
Regards,
K-BIKE
