Know how: Polishing Diesel

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The parts are mounted on a slab of plywood which is bolted to the inside of a locker

The parts are mounted on a slab of plywood which is bolted to the inside of a locker

Portland, Oregon. The fuel nozzle at the dock had a recoil like a small caliber pistol. The fuel tank sits tightly immediately beneath the cockpit of my sailboat. The fill pipe, if you want to call it that is 3in long. I couldn’t just squeeze it off, the fuel hit the tank point blank, certain to disturb debris sitting on the bottom. The tank is the real McCoy, 40-years-old and galvanized.

Sure enough, with 40 gal onboard and who knows what bergie-bits swirling around, when I put the accelerator up a bit to get away from the dock, the RPM wavered ever so slightly. I’d heard that “wavering” before. I jerked the boat back against the dock. The engine shuddered horribly, painful to witness and died. Truth be known: I inherited a filthy tank. Not a good thing for a guy whose future plans include crossing the Columbia Bar.

I threw the selector handle over on the double Racors to draw from the other filter. Hit the starter. Again. My Vetus 4.15 could do no more than feign life. On the river that day the wind was not here but there, the current everywhere, getting home meant motorsailing and neither one was fun.

Here’s how I laid out the fuel polishing system. Note the two vents. The engine fuel return line is not shown

Here’s how I laid out the fuel polishing system. Note the two vents. The engine fuel return line is not shown

When I bought the boat, the Racor filters were so filthy it was a struggle pulling them out of the bowls. At the time a dock-side fuel polisher man suggested that I replace the tank. That’s what he said. What I heard was: “Take a Sawzall to the cockpit.” He saw me fainting, “Or install something to clean the fuel.” Because the fuel dock was not the first scenario with problem fuel I decided to go ahead, but on my budget, it would be homemade.

As I see it, fuel traveling from the tank to primary and secondary filters and on to the fuel pump is filtered once, only while the engine is running. Despite the beneficial agitation that occurs during rolling and pitching, diesel on sailboats sits mostly settling and deteriorating.

I define fuel polishing as pulling fuel from the tank via an independent pump, putting it through a separate filter and sending it back to the tank- over and over again—engine running or not.

As a boat project the concept was simple: cut a T fuel fitting into the fuel supply line at the tank and run a hose off to a special filter/separator, a shut-off and a pump. Now return the fuel to another T high up on the fuel fill hose somewhere near the deck fill. Some boats can, indeed, be this simple. Mine required a bit more work, but with modest skills—no special tools—observing safe practice standards, anyone can accomplish this fun, inexpensive and value-adding upgrade.

Clockwise from top left: I had to cut a hole in the cockpit in order to replace the old vent fitting; it’s now accessible through an inspection plate; this walnut-sized filter lives in the fuel pump; this temporary 50 micron filter let me see the crud piling up

Clockwise from top left: I had to cut a hole in the cockpit in order to replace the old vent fitting; it’s now accessible through an inspection plate; this walnut-sized filter lives in the fuel pump; this temporary 50 micron filter let me see the crud piling up

Equipment already on the boat was a double Racor Primary 75/500FGX 30 micron diesel filter set. The secondary filter (on the engine) was an economical automotive substitute for what the manufacturer specified. There was another filter hidden inside the fuel pump that the manual said was good for 500 hours. This little critter alone could have caused the drama at the fuel dock.

Under my regime the filters have been replaced seasonally and that should make a polisher unnecessary. But the timely changing of filters is apparently not going to bring a tank that’s been neglected for years to an acceptable level of contamination.

Setting Up the System

As the main piece of equipment for my fuel polishing system, I found a used Racor 200 FG filter body and gave it a ready-for-surgery cleaning. The rebuild kit and filter elements were easy to find. The low-output fuel pump, suitable for bio-diesel (not the type for fuel injection systems), came from my local auto parts store.

I mounted the filters, pump and switch/fuse box on a slab of plywood, leaving the hoses long, and bolted it with wing nuts to a bulkhead inside a seat locker. It takes only a few minutes to pull the whole thing out for service.

Then I had to work out how to get the fuel from the tank to the polisher and back again.

It was easy to install a T-piece into the fuel supply hose at the tank and run a branch to the new filter. Getting the fuel back to the tank was more involved. I chose not to cut into the fuel return line from the injectors, and of course, it was impossible to T into the tank’s fill pipe. The only way to get the fuel back into the tank was via the tank vent and to achieve that, I cut a hole in the cockpit deck so that I could remove the old 3/8in fitting and install a 5/8in fitting. The greater diameter would help with venting.

This left me with the issue of diesel running one way in a hose, and vapors flowing through in the opposite direction. I decided to copy the “wet vents” seen in commercial/industrial applications. To accommodate the two-way traffic with plenty of margin, the new arrangement has two venting points. First, the hose taking fuel back to the tank joins with the original transom vent. This vents the 8ft or so of plumbing involved. Near the tank, I teed an additional vent into the line to handle the tank itself. With two vents, and pump output a modest 4-7 PSI, fuel does not fill the entire volume of the hose.

fuelPolishing12-2018

Ready to go

To start with, I installed an inexpensive 50 micron plastic see-through filter just to enjoy seeing the crud come through. Eight hours later it was loaded with filth, as was the 2 micron element in the Racor 200. I replaced both filters. Thirty hours later the sludge accumulation began to taper down somewhat. The third set should work for about 100 hours. The 2 micron element inside the Racor 200 is purposely fine, but if it clogs it won’t stop the engine.

I soon replaced the cheap plastic see-though filter with Ta metal 141 micron- “big junk catcher.” The 2 micron element in the Racor 200 is the “nitpicker.”

The boat’s twin Racor filters now have 10 micron elements instead of 30 microns. On the engine, I run the filter specified by the engine manufacturer, despite its exorbitant cost. These filters, plus the 500 hour filter in the engine’s fuel pump, are changed seasonally, regardless.

My home made polisher is doing its job. Replacing the tank will be a project for the future. In the meantime, it’s full speed ahead with cruising plans. 

Costs

Facet 610-1050 Posi-Flow fuel pump $60

Hoses 5/16, 1/2, 5/8 fuel grade $35

Racor 200 FGM filter/separator Purchased used $60

Racor 200 2 micron filter for above $20

Fuel fittings, hose cover, clamps $30

Shut-off valve $50

Napa plastic filter #23002, testing $4

Napa metal filter #3270, long term $15

Mounting board/expendables/switch/fuse box $35

Total $309

Not included—Cost of inspection plate

The author’s Cape Carib 33 ketch is wintering in Astoria, Oregon.

December 2017

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