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30 micron racor filter... 10 micron?

Aug 23, 2014
Catalina 310 Guntersville, Alabama
I presently have a 30 micron racor fuel filter but in changing it out due to a leak I am hearing that many run a 10 micron filter. Should I stay with the 30 or is 10 the way to go these days. This is a diesel 2003 Universal 25mxp. There is also a fuel filter on the engine. Thanks.
Jan 4, 2006
Hunter 310 West Vancouver, B.C.
Probably depends on your fuel supply.

If you have access to high throughput diesel vendors, a 10 micron is fine and won't plug up too early. Your secondary filter last longer as well. If your fuel is dirty, go with a 30 micron and it will last longer.

All comes down to how often you want to change your filters. That 1-2 micron secondary filter at the engine will always do its job, but filter changes .................. aye, there's the rub.
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Mar 2, 2008
Cal 25 mk II T-Bird Marina, West Vancouver
As others have said it comes down to how clean your fuel is and how easy it is to change your filters. My secondary filter element is the standard Yanmar 10 micron and I use a 2 micron Racor primary filter element with a vacuum plugged filter indicator. I installed a new fuel tank (leaking aluminum with a larger poly tank), new fuel lines and changed both filters when I bought the boat ten years ago and again this summer after 259 hrs. Not because they need changing but because it has been ten years. My Racor is many times easier and quicker to change than the Yanmar secondary plus I’ve got the indicator.
May 24, 2004
CC 30 South Florida
I would stay with the 30 micron as the secondary filter found downstream is likely a 10 micron. This way they will divide the work and together last much longer. The 30 micron will catch the larger particles and allow the 10 micron to catch the smaller ones. A 10 microm by itself doing all the work will clog much quicker. Diesel fuel can be dirty especially when boat motion in rough seas may dislodge sediments from the bottom of the tank and having to change clogged filters underway in those conditions is not fun.


Jun 4, 2009
Pearson 530 Admiralty Bay, Bequia SVG
On most engines the secondary filter is much more difficult to change than the Racor, it being a top loading filter housing. Therefore. I'd go with the 10 in the Racor and expect to change it 4 to 6 times as often as your secondary, depending on your fuel quality.
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Feb 14, 2014
Hunter 430 Waveland, MS
Tip: Cigarette smoke is ≈10 micron. You can see a flashlight beam light inside a glass mason jar of diesel if > 4 micron particles are present.

Probably depends on your fuel supply.
Make sure you have an algaecide if your supplier doesn't put some in.

I have a hard time conceiving anything smaller than 30 micron plugging/damaging my fuel system.
Feb 6, 1998
Canadian Sailcraft 36T Casco Bay, ME

There are no on-engine/secondary Yanmar or Westerbeke / Universal filters that are 2 or 3µM. Universal (Kubota engines) spin on filters are 25µM rated. Westerbeke cartridge filters (Mitsubishi etc. engines) are 15-17µM. Yanmar on-engine/secondary filters are 10-15µM or 15µM... (note none of these are "absolute" ratings)

A 10µM filters is fine, but will plug faster than a 30µM.. None of these engines makers wants you to use a 2µM as a primary.

Dec 25, 2000
Hunter Passage 42 Shelter Bay, WA
Each 1991 engine (4JH2-TE main-1900 hours, Onan 8kw Genset-450 hours) has a ten micron Racor filter between the fuel tank and engine fuel filter. The Yanmar has a ten micron spin-on canister filter. I replaced the OEM two micron Genset (three cylinder Kubota) cartridge filter with a six micron canister when it became clogged. Both start and run well.