Looking for the best flowing and filtering water separator that will fit stock merc. 454mag MPI's or 502 mag MPI's.

I would like to know this as well. I believe Sierra makes a 10 micron water seperator filter that replaces the Mercury 25 micron. I am not sure if the flow is equal or any draw backs going to a finer filter, like starving the engine or clogging the filter sooner.

Ayuh,.... The stock units will flow more fuel than yer motor can burn,....

Clean filters are the key,....

These are, in my opinion, the best filter out there for your application. http://fstperformance.com/

I believe you are correct. Those filters were OE on the Mercury 800's, 1075's and 1200's

Would you believe Mercury has a new filter? It actually looks pretty good on paper.

I'll find the part number.

If you ever cut open the stock OEM Mercruiser fuel / water sep filter you would be surprised. We have cut open 100's. They are poor quality. Especially after fuel sits in them for sometime.

They have a vinyl / rubber pad dead center bottom internally of the filter that deteriorates and turns like a black gel substances. Also they have poor sealing glue in globs around the metal end caps but not every filter has this.

Next important tip is look under side of the filter mounting pad you might be surprised in that area as well. Rust and or aluminum oxide build up and sometimes very heavy.

The middle portion of the filter mounting pad can form rust way up in that section as that is your fuel outlet portion after the filter. Just get an inspection mirror or take the whole mounting pad off to see if you have crap built up. Its easier to see when its off and of course turned upside down.

Racor with the metal base / water drain or Wix would be good choices.

do u have a wix number by chance?

Not a fan of wix anymore.

For the money Sierra - very even spaced pleats, expoxy coated internally never any corrosion, no rubber or plastic or no glue that dissolves to jack with upper fuel system components.

Wix uneven spaced pleats, can corrode internally over time, and a plastic piece that forms to the spring that deteriorates over time. Prob my post here is going to create an argument. Sorry guys I cut marine fuel filters open daily and see the end results to know better whats poor, whats middle of the road and what holds up really well without issues. . .

Next upgrade is Racor and for I/O's boats --- YOU MUST have the metal bottoms NOT plastic bottoms installed on the Racor filters. CG approved is the metal bottoms for I/Os mounted inside the engine compartment.

Next the highest up grade is FST Filters. These filters years ago had another name until FST bought them out about 5 years ago.

Merc black side OEM filters is one of the worst quality filters you can buy, they corrode internally as well. Complete junk. Even if you cut these open when brand new,one will see how poor the quality is.

Last season for WIX for me that's for sure! One thing worth noting on the FST's is you need a new filter head for the stock MPI apps I think but that may have changed since I last looked.