FUEL IN A SECOND FILTER

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

NIGEL CALDER REPLIES

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