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The Fuel Tool

"Jim,” I yelled, peering into the fog. “We’re losin’ power. What the heck’s goin’ on?” There was a young first-assistant engineer on board and he was fairly flaky. He’d put new elements in our duplex fuel filtering system, he swore, but I was suspicious, primarily because our big Electro-Motive-Diesels were beginning to surge rhythmically, a dire development considering we were working our way across a broad convergence of shipping lanes. Jim hit the trail for the engine room posthaste.

Dustups like this were common back in the day, unfortunately. “Oilfield yachting,” as I used to call it, got a little loose occasionally. But then again, I still hear about similar happenings today—where some boat somewhere gets into trouble, due to a diesel-fuel filtering system that clogs up for some ungainly reason, turns uncooperative and eventually shuts down an engine or two, often at the worst possible moment.

The most straightforward way to prevent this sort of thing, of course, is to enhance a given fuel filtering system with a vacuum gauge. Typically, you splice the device into the outlet side of the system (between the primary fuel filter and the engine) so it directly measures the vacuum (or suction) generated by the engine’s lift pump as it pulls fuel from the filter.

The black needle indicates vacuum and the red max pressure. Thick red? Changeout.

The black needle indicates vacuum and the red max pressure. Thick red? Changeout.

Actually, using a vacuum gauge is easy. You start by popping (a euphemism for an often oily, smelly, messy job) a new filter element into your filter canister so your gauge can measure exactly how much vacuum exists between a clean, unrestricted filter and your engine at service speed—this gives you a baseline. Then, you simply monitor increases in vacuum as the filter element inevitably fills with dirt and debris, a process that must be eventually terminated (by popping in another new filter element) so engine-bound fuel doesn’t totally aerate and cause the lift pump to struggle and the engine to fail.

Vacuum gauges these days are way more sophisticated than they used to be. More to the point, most are equipped with two indicator needles, not just one. The first measures vacuum in inches of mercury (“Hg”) and the second registers the highest vacuum reading that occurs during a given amount of run time, thereby precluding the need to make personal visits to a hot, noisy engine room to check vacuum levels while underway.

Additional features include bezel-mounted markers that can be set to indicate the vacuum reading that requires a filter-element changeout based on either an engine manufacturer’s recommendation or a boater’s personal experience; reset buttons that obviate all prior readings; and pressure-relief valves that boost gauge accuracy by adjusting to changes in ambient barometric pressure.

And oh, about Jim. Under the watchful eye of a sleep-deprived chief engineer, he soon removed the grungy filter elements in our duplex filtering system and replaced them with brand-new ones. Which made both me and our EMDs very happy.

For more tips like this, visit the Vetus-Maxwell DIY Workbench at

Capt. Bill Pike is deputy editor of our sister publication Power & Motoryacht magazine.