Trying to understand the fuel filters on my boat (twin Ford Lehman SP135s) and filters in general. As mentioned in a previous thread I have dual Racors that have 30 micron elements then two on-board engine filters with 5-7 microns. What I don't understand is why 30 micron in the Racors and why only filter down to 5-7 mics when 2 mics are available. It would seem that my setup allows a lot of "stuff" to get through to the on-boards which are more difficult to change out. Then there is stuff less than 5-7 mics that get into the injectors/engine. Is there a reason that I wouldn't want to get as much filtration as possible as soon as possible in the system? I know that filtering down to 2 would cause more frequent filter changes but...that would seem to be a good thing? What am I missing?
Thanks for any comments!
You can do anything you want and will get plenty of advice, some of it ignorant like mine.
It seems to me there are two camps to this continued debate on filtering. The first camp is the one in which I fall that says that you should filter the fuel as the engine manufacturer intended. Folks a lot smarter than I and with the appropriate engineering background came up with those recommendations for a reason. They also specified fuel filtration that matched the fuel pumps in the engines. So I would say look at your engine information and see what they suggest. If they suggest 30 micron primarily filtering with 5 micron secondary, then do that.
The other camp feels that, in general, you can't have too much filtering. If 30 micron filtering is good, 20 is better and 2 is best. They never want to touch their on-engine filter so want the primaries to do all the filtering so the on secondaries never get dirty. They distrust the manufacturing recommendations for a variety of reasons ranging from being too general and not specific to their installation (not a bad reason actually) to some vague conspiracy theories involving lawyers, filter manufactures, and black helicopters.
Nothing wrong with highly filtered fuel, but there are two potential problems I can see with using 2 micron primary and secondary filters. The first as you mentioned is more frequent filter changes. Not a really bad thing, but if your engine manufacturer doesn't care about particle size before 5 microns, do you need to filter down to 2 microns? The more important question is whether your fuel system can handle the added restriction of 2 micron filtration when it was designed for 5 micron filtration. It takes more effort to pump fuel through two, 2 micron filters than it would through a 30 and a 5 micron filter.
In the few minutes it has taken me to type this, I won't be surprised if you get 5-6 responses giving you 5-6 different answers.
To read something from someone that actually knows about what he writes, check this out.
https://www.sbmar.com/articles/fuel-filtration/
https://www.sbmar.com/articles/marine-fuel-filtration-the-seaboard-way/