As of March 1999, there were two Nauticats with fitted fuel polishing systems. Both skippers are happy with the results. Dick Bishop reports that he circulates their fuel about every two weeks.
I also have a report from a captain of a trawler, who has done extensive testing on this subject. He does not lay all the credit for cleaning his fuel to the Fuel Mag. It is not a filter.
He theorizes that the circulation rate and frequency has a lot to do with keeping the creosote in suspension, and the 2-micron Racor 500 catches the dirt and debris, while the Fuel Mag does a job on the bugs.
50 GPH is his recommended pumping rate, which is about 10 times the engine pumping rate for a Lehman 6/140Hp. 35 GPH would be an adequate rate for the 80 and 90Hp Lehman in most of our boats.
I'd say this is well worth doing, if for no other reason than to gain the peace of mind that rough seas will not bring forth trouble from deep in our tanks! Bob Smith says the best thing you can do for your diesel engine is to give it clean fuel.
Building a polishing system requires some careful planning and attention to good practice. Use only high quality valves and fittings lubricated with seal compound not teflon tape. Use only USCG rated tubing and strive for zero leaks. Mount all the components on a panel of nonabsorbent material and mount it on a bulkhead easy to get at. Turn the tubing out of the way and secure it with wire ties.
In the illustration, both tank select valves are existing, so only two new 3-way valves are needed. When fuel polishing, both bypass valves are in the (b) position and flow is blocked through the normal path. In the (a) position both ends of the circulation path are isolated, preventing any possibility of air being drawn into the line through the tank vents.