Fuel filters will be better micron ratings. Granted some oil filters are the same micron rating but not water blocking/absorbing or seperator. After centrifuging I pass everything through a 1micron sock filter then use the stock truck filter. They make a 98% effiecent sock filters (i just use a regular 1micron). It would be hard to use those as a gravity setup, but a filter housing would be better. Utah biodiesel has a great selection. There are some water filters that use sock filters and work well when used oil safe seals. After passing thought sock filter I feel like the stock filter is adequate then stock filter on the truck is good. Just centrifuging it till it stops pulling stuff out you are doing world better.
Lots of wvo guys/girls use racor 1000fh(or 900fh, 500fh, marine 1000ma). Filters are economical. Another brand is davco. Davco 382. Options of coolant heat or electric heat which is also cool. Lots of used ones at truck scrap yards or ebay. Filters are similar costs to stock fuel filters.
They are sizing racor or davco to still have the adequate flow when cold thick wvo/wmo. If you want a spin-on setup there are biodiesel filters. I am looking for an old picture. But lots of options out there.
I don't really believe this, but I have been told that the stock filter rating is as good as you need to take it. Anything smaller would pass through without damage. Hedging bets is good so I try to go as clean as I can. Catapilar uses a lot of 2micron. Aviation uses 1micron&dewatered on the fuel farms and trucks, then most turbines engines have 10micron(might vary) fuel filters on board. Fuel is also filtered on deliver, again loading trucks and then again into aircraft. So it is very clean and dry. That mentality makes me think that cleaner then oem filter is benificial and the filter is to catch the big stuff. That is just my thought process. I wonder how much they pull out of bunker oil before sending it through those big marine engines. haha