SAIL - - Ask Sail -

Q: I have a Yan­mar 3YM30 pow­er­ing our Catalina 320 and have been think­ing of adding a sec­ond pri­mary Ra­cor fuel fil­ter and set­ting things up so that when one fil­ter starts to show foul­ing, valves can be turned to en­gage the other fil­ter. For this to work, how­ever, the un­used fil­ter sys­tem would need to be primed and ready to go at the throw of a cou­ple of valves. My ques­tion is: how long can a fil­ter re­main primed with fuel be­fore the fil­ter or fuel de­grades? Learn­ing the hard way, I have made it a habit of chang­ing my fuel fil­ter when I change the oil and its fil­ter ev­ery 100 hours—a process that has kept me out of trou­ble—that, and a clean fuel tank. Might it be that a sec­ond Ra­cor is overkill? Ron­ald Hodel, sail­mail@sail­magazine.com


If the fuel tank is kept clean, and given the low an­nual en­gine run hours on most sail­boats, a sec­ond pri­mary fil­ter, valved so that you can keep the en­gine run­ning while chang­ing one or the other fil­ter, is overkill. The pre­sup­po­si­tion here is you have cleaned up the fuel tank and kept it clean, which in my opin­ion is the sin­gle most im­por­tant item in marine diesel main­te­nance. Given a clean tank, un­less you take on se­ri­ously con­tam­i­nated fuel, chang­ing the pri­mary fil­ter ev­ery 100 hours or so is also overkill. The fil­ter should run 600 hours, or what­ever is rec­om­mended in your en­gine man­ual, and still look clean when changed. A use­ful and rel­a­tively in­ex­pen­sive item to add to the fil­ter is a vac­uum gauge that will warn you if the fil­ter is be­gin­ning to plug. You want one with a tracer nee­dle that will in­di­cate the high­est vac­uum seen when the en­gine is run­ning after the en­gine has shut down.

Should you de­cide to add a sec­ond fil­ter, I would not let fuel sit in it for months at a time. The is­sue here is not so much the fuel de­grad­ing (so long as it does not con­tain bio­fu­els you could let it sit a year or so and it would be OK) but the fact that there may be mi­cro­scopic quan­ti­ties of wa­ter en­trained in the fuel that will rust out the fil­ter’s in­ter­nal parts. If there is a bio­fuel com­po­nent to the fuel, this also changes ev­ery­thing. The bio-com­po­nent de­grades faster than con­ven­tional diesel and holds con­sid­er­ably more wa­ter. You should not let this sit for more than a month or two, in­clud­ing in your fuel tank or any­where else in your fuel and in­jec­tion sys­tem. s

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