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Not much surface area - easy to get plugged up. How many micron. If it was 100 micron maybe not a restriction to flow but it is probably not that open.

that looks like the filter in a oberg filter,i used one back in my drag boat days.it is designed to be checked after every pass for early detection of engine problem.i would not use that in a marine endurance application.

The mesh pre-filter was sitting under a fram racing hp4 filter. I didn't put the prefilter back in place with the new wix racing filter going on. I too was concerned they may restrict flow. Both my engines were reportedly rebuilt to varying extent before I took ownership of the boat and maybe these were just put in place to trap articles from an engine settling in and were intended to be removed after the breakin period/first oil change after rebuild?

I really don't see the need for one

Ney.

What is an oil filter for ?

If you are looking for particles, cut one open.

Bingo. I use one as a monitor during the first ten hours or so of operation after a build. I pull the filter and have a look for anything big on the screen. I then clean and reassemble. I'm not changing the filter at this point; just checking the screen. At ten hours I change the oil and cut open the filter to inspect. The screen goes back in my toolbox at that point.