FilterMag Oil Filter Magnet: Outboard Fitment & Long-Term Use
Updated: Sep 4
This is one for the 4-stroke crowd—whether it is hanging on the transom or sitting under the hood of your tow vehicle or RV. FilterMag is a product I have personally used since about 2004 on both my outboards and tow vehicles (or “Skiff Mules”), which have also served as my daily drivers.
The idea behind FilterMag is simple and practical. Anyone who has spent time turning wrenches has probably seen magnetic drain plugs used in transmissions, differentials, and outboard lower units to help capture fine ferrous particles. FilterMag applies that same basic idea to the outside of a spin-on oil filter.
The FilterMag oil filter magnet adds another layer of protection by helping capture fine ferrous wear particles.
Here is a short video that explains how it works and how it can help reduce wear on expensive—and sometimes hard-to-replace—internal engine components.
As discussed in this pre-lube pump quick tip, there are a few ways to help reduce engine wear during startup, including some simple approaches for certain outboard applications. FilterMag takes a different approach by helping capture fine ferrous wear particles in the oil filter before they can continue circulating through the engine.
Why Startup Wear Matters
FilterMag can help capture ferrous wear particles shed by steel and iron engine components such as piston rings, camshafts, timing components, and portions of the valve train. Those particles are then held against the filter media rather than continuing to circulate through the lubrication system.
Startup is one of the periods when an engine can experience increased wear because full oil pressure has not yet been established. A residual oil film remains on internal components, but getting pressurized oil flowing quickly is one reason proper oil viscosity, a quality filter, and regular maintenance matter.
Case in point: how many times have you turned the key on a truck and heard a brief “Clack, Clack, Clack” or ticking noise from the top of the engine just after startup? That can happen while oil pressure reaches the upper valve train or hydraulic lifters refill. It is a good reminder of how quickly the lubrication system has to go to work every time an engine starts.
Although FilterMag was originally developed for automotive and commercial vehicle applications, the same basic principle can also apply to many spin-on outboard oil filters. The key is proper fitment: you need the correct FilterMag model and enough clearance around the filter for proper installation.
FilterMag Oil Filter Magnet Fitment and Clearance”
Speaking of FilterMag clearance, years ago the RA-250 model fit perfectly on the stock Honda outboard oil filter used on my 2004 BF150. I mounted one FilterMag on the bottom of the filter and used the heavy-duty model simply to make sure it stayed put while running rough passes. Never had a problem with that setup, even after plenty of hard running in rough water—and occasionally getting everything, including the outboard, airborne. 😁
That kind of clearance is not available on every outboard. Filter size, engine-block castings, hoses, wiring, and nearby attachment points can all limit the space available for one—or sometimes two—FilterMag units. Proper fitment matters more than trying to force a particular installation.
Case in point: when I was figuring out which FilterMag to use on my previous Yamaha F70, the available clearance was pretty tight. The F70 uses a relatively small oil filter, and there was not enough room around it for a FilterMag on both sides. One unit would fit cleanly on the bottom of the filter, though, which was fine with me. That same basic installation had already worked well for many years on my previous Honda BF150.
I called FilterMag Technical—great folks and always willing to help. They did not have, and still do not have, a specific outboard-engine catalog, so I sent them a photo of the oil filter on my then-2013 Yamaha F70. They recommended the SS-250 model, and it fit—just barely!
As you can see from the Yamaha F70 photo above, there was not much clearance around the oil filter. I could still get enough grip on the filter to remove it, but it was tight. That is something to keep in mind during installation—an oil filter should never be over-tightened, especially when limited clearance means you may need a little extra finesse to remove it at the next oil change.
Clearance on our newer Yamaha 115 SHO is not much better, and once again there is only enough room for one FilterMag on the oil filter. That does not concern me, though. As the video below demonstrates, even a single FilterMag can capture a surprising amount of fine ferrous material.
Choosing the Right FilterMag
If your specific outboard application is not listed, the easiest way to narrow down the correct FilterMag is to measure the oil filter or locate its part number. You can then cross-reference those dimensions with the FilterMag model and fitment information on their website. And if clearance is especially tight, it never hurts to contact FilterMag directly—as I did with my Yamaha F70.
What About Cartridge-Style Oil Filters?
Cartridge-style oil filters are a little different because there is no exposed steel spin-on canister for the FilterMag to clamp around. Depending on the design and available clearance, though, one or more FilterMag units may still be used around a suitable metal filter housing or with another approved installation method. FilterMag has additional information on cartridge-filter applications and installation options for those setups.
What Is FilterMag Actually Catching?
So, what is FilterMag actually doing? It helps capture fine ferrous wear particles and hold them against the oil filter housing and media rather than allowing them to continue circulating through the lubrication system. It does not replace the oil filter itself—it simply adds another way to capture magnetic debris that conventional filtration may not immediately remove.
Final Thoughts
Those fine ferrous particles are exactly what FilterMag is designed to help capture before they continue circulating through an expensive engine. It is a simple idea, but after using FilterMag for years on both outboards and tow vehicles, it is one more layer of protection I am comfortable keeping in place.
And if you decide to order one, let FilterMag know Flats Nation sent you and use promo code FlatsNation10 to receive 10% off your order. 😁
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Tight Lines, and God Bless!
Dave and the Team
