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How to Rebuild a Fuel-Water Separator

Parker Racor FG500 fuel-water separator

Sniff, Sniff, Sniff

How to rebuild a Parker Racor FG500 fuel-water separator that’s leaking a little diesel.

You see lots of Parker Racor FG500 fuel-water separators kicking around the waterfront, both on new boats (mostly protecting gensets) and on older ones (like my 32-foot Grand Banks trawler Betty Jane), where the trusty little device (photo 1) helps stop water and other contaminants from getting into main engines.

The FG500’s a venerable product but not a maintenance-free one. Just a few months ago, upon catching an errant hydrocarbony whiff in my engine room, I observed the faint leaking of diesel fuel down the side of my admittedly old (like 26 years old, I believe) unit. At first I suspected the topside lid had somehow loosened and was spilling fuel ever so slightly, letting it slide down the side of the canister. But closer inspection revealed the source of the leak was instead somewhere near the metal ring that holds the glass bowl in place. A teardown ensued, followed by a rebuild.

My first step was, of course, shutting off the fuel valves on both of my two fuel tanks. Then I put a bucket under the unit and removed the plastic drain assembly (which, oh happy day, I serendipitously discovered needed immediate replacement due to a dicey little crack in its side) from the bottom of the bowl using an adjustable wrench, thereby allowing quite a bit of fuel to whoosh into the bucket (photo 2). Loosening the plastic drain assembly meant rotating it counterclockwise, by the way. Backing off the T-handle at the top of the unit and removing the topside lid, as well as the filter element inside the canister, finished the draining process in short order.

Parker Racor FG500 fuel-water separator photo 2

The next step was the tough one. The four, Phillips-head machine screws holding the metal ring (and the glass bowl) in place at the bottom of the unit had not been removed in many years and were flat-out frozen in place. So I gave each screw a shot of Kano Laboratories Aero Kroil (, the fastest, most trustworthy penetrating oil I know of, waited a minute or two, and then used an appropriately sized, ratchet-equipped Phillips-head screwdriver (and plenty of pressure) to back the screws out. They came away rather satisfyingly, I must say.

When I removed the metal ring it was immediately obvious that the gasket that seals the ring and bowl to the canister bottom was the problem—it was shot. Luckily however, in preparation for such a finding, I’d already purchased a new one (shown in my fingers, photo 3), along with lots of other paraphernalia in the “Gasket Pack” and new “Drain Assembly” I’d purchased from Parker Racor for the modest sum of $56 apiece. Yeah, to save money, I’d tried to buy just the gasket and the new drain assembly for starters, but no dice. I wound up having to buy the rest of the stuff as well. But hey, at least the extra lid gaskets (black) and the little gaskets that seal the T-handle base (reddish orange) from the Gasket Pack may come in handy some day.

Parker Racor FG500 fuel-water separator photo 3

Lighter by a few dollars, I was nevertheless rollin’ now. The turbine centrifuge/conical baffle component inside the glass bowl came out readily and I cleaned it in fresh diesel, being careful not to lose its lightweight “check ball.” After installing a new check-ball seal (from the Gasket Pack), the spic-and-span check ball, and a new bowl gasket (again, the one shown in my fingers above), I reattached the bowl using the machine screws and the metal ring. Then I secured the new drain assembly to the bottom of the bowl with the supplied gasket, remembering to tighten the assembly by turning clockwise.

Swapping out the old T-handle and lid gaskets for new and reinstalling the centrifuge and a new filter element pretty much finished the project. While the lid was still off, I opened one of my two fuel valves slightly and let fuel pressure fill the canister almost to the top. Then I returned the valve to the off position temporarily and finished the job with a turkey baster (photo 4). After securing the lid and opening both fuel valves all the way, I topped off the festivities by bleeding the secondary fuel filters on my Lehman SP135 diesel so there was no chance I’d air lock the old girl. Better safe than sorry, I always say.

Tough job? No, kinda fun actually. Took me about two hours. The reliable old Lehman cranked up and ran like she always does afterwards. And I suspect she’ll continue to run that way. With nary a hydrocarbony whiff.

Parker Racor FG500 fuel-water separator photo 4

This article originally appeared in the May 2014 issue of Power & Motoryacht magazine.