Our field tanks have reached a level of crud that's untenable. However, talk to three old salts and you'll get four good solutions.
As noted in Easter and Rebirth, our fuel tanks aren't feeding properly. On Easter Sunday, we didn't know what was wrong. Thanks to American Diesel Corporation, we now have a diagnostic procedure, as shown in the photo above. This applies the Divide and Conquer principle to diesel engines.
It took a lot of bleeding and priming, but, eventually, Mr. Lehman started and ran from the jerry can. Ran beautifully, by the way. How beautifully?
Vacuum pressure dropped to zero. (This picture is a little cryptic because the vacuum gauge has three indicators: a black current pressure, a red maximum pressure seen recently and another red "change your filters" indicator. Plus the back of the gauge has a yellow and red bands.)
When we were connected to the fuel tanks, the pressure was on the order of -20" Hg—read "clogged"—for both filters. Both! Usually one filter is clogged and the other still works because the clog is the filter itself.
The jerry-can test confirms that the tanks themselves are the root cause, not the new filters or the engine-room plumbing. What next?
The Fix is In
We got a lot of candidate fixes.
Polish the fuel. Pump it through some filters and replace it in the tanks. Think $75/hr times 4 hours per tank.
Steam-clean the tanks. Again, $75/hr times 4 hours per tank. Plus the job will probably destroy one or two shop-vacs that we have to buy. And the fuel is disposed of—to the tune of $7 per gallon for 125 gallons!
Back-flush the fuel pickup to knock out what's blocking it. (Is this a solution? Or just a hack?)
Only buy the fuel you think you'll use and dispose of the rest before winter haulout. (What deeper mystic knowledge is required to make this judgement call accurately?)
The skipper of Discovery showed me a new state-of-the-art fuel pickup tube. This sprang loose some thinking on yet another solution. Also, Tom of Monday Morning (Tornado Tom) told me about his tank's pickup tubes being fouled. There's a pattern here.
Another skipper weighed in with this: 80% of the fuel going through the filters returns to the tank. When you burn one gallon each hour, four gallons are pulled from the tank and returned. That fuel is, in effect, polished during normal engine operations. Yes, it takes 20 hours to polish 75 gallons of fuel. No, it isn't the 500 GPH high-pressure system that fuel polishing services use to knock goo off the sides of the tanks.
Root Cause Analysis
Once we knew it was the tank, I took a further step. I put my Moeller Primer Bulb into the fuel line and pumped fuel back into the tank in reverse. It took a bunch of pumps to get anything to flow backwards through the fuel line. Eventually, thought, I blew the crud out of the plumbing and pickup tube and back into the tank where it can settle to the bottom, only to be picked up again.
I took a sample of what was in the tank and there are some flakes of something drifting around. A collection of those flakes appear to have fouled the pickup tube, rendering the tank useless and leading to our engine death on Sunday.
Our fuel system uses 30-year old bronze fittings. We've already had fittings fail. In Hubris? or Shakedown Cruise? we struggled with failed fittings. In Big Improvements we noted the new filters resulting from that failure.
Our fuel tanks also use 30-year-old ¼" OD bronze. It's probably time to move on before they crack and leak.
First, I'm getting to be a cracker-jack fuel bleeding wizard. There are limits to my skills, but I'm eventually able to get Mr. Lehman to start.
The new Racor spin-off filters are a delight to change and reprime. With two filters one can—in principle—change a clogged filter while the engine continues to chug on the other. W00t w00t.
More importantly, the "bypass the tanks and use a jerry can" technique works quite well, once you get everything hooked up and primed. We have our official bypass plumbing now. In the event of a future pickup tube clog, we can always sail up to the mouth of Jackson creek, drop the hook and spend a few hours rigging the bypass.
Blowing out the crud by back-flushing works as an additional hack. It's never a solution, but we now know the symptoms of clogged intake tube. It does require some care to get fuel back into the fuel lines without siphoning the entire fuel tank into the bilge. Having done it once, we can certainly do it again.
We've decided that the best move is to remove as much of the old, rigid tubing as we can. We can replace it with Coast Guard-approved fuel line hose. The work is messy and annoying, but not too difficult. There's a fuel feed, fuel return and a ventilation line from each tank. The hard part is controlling spillage.
While we're at it, a more complete solution is to pry the inspection plate off each tank, tap out new holes and replace the hardware on the tank with new, ⅜" aluminum and Teflon hardware. This requires a competent machinist to tap new the holes in the existing plate.
A future upgrade is a "day tank". We have to measure the lazarette carefully, but we might be able to put a 20 gallon "side tank" (36" × 19" × 8" with 3" clearance required) inside the lazarette. We'd need to frame it up carefully to prevent damage. We'd also need some kind of fuel transfer pump with a pair of T fitting and valves. This pump would be inserted in parallel with Mr. Lehman (after the primary filters.)