Monday, November 5, 2012

It's Deja Vu All Over Again

We recently had renewed problems with the port engine. The symptoms were the same: when running at about 2500 RPM, the engine would lose RPM, dropping to about 1100, then resume 2500 RPM, with a cycle time of about 15 seconds. The trip down the Chesapeake had us pitching up and down with following seas. Crossing Port Royal Sound was the same, only we were going into the wind and waves. Then we went out the Savannah River and down the coast, coming in at St. Catherine's Sound. The wind and waves were from the west and it caused a lot of rolling, which causes fuel to slosh between the three partitions in the tank. This was the test that we were waiting for.

So it was time to open the inspection port and see what was going on in the tank. We pulled into St. Augustine, FL with the port tank about 1/4 full (10 gal). We found that the tank had a few pieces of bio scum in the bottom that had migrated from the sides into the center partition. We also found that the Racor 10 micron filter was black, filled with filtered scum. We suspect that the electric fuel pump filter is also clogged from the time when it was in the line between the tank and the Racor. In preparation for this trip, we moved the electric fuel pump to the output side of the Racor, where is now resides, pulling fuel through the Racor and feeding the low pressure pump. Our setup is shown in this photo. There is also a valve that allows us to select the fuel pickup source, which can be either the main pickup or the fuel priming bulb pickup (or both, if we put the valve in the mid-way position). The other advantage of this setup is that we can use the priming bulb to pump fuel back into the main pickup, just to convince ourselves that there is nothing blocking it.

The filtering system is working as designed and desired. We moved the fuel into the stbd tank using a drill pump, pulling through the Racor filter - basically polishing the fuel as we pumped it from one tank to the other. We cleaned out the bottom of the tank, replaced the electric fuel pump filter (100 micron) with a straight through fitting (relying on the Racor to filter the fuel prior to getting to the electric fuel pump), and we should be back in business. We refueled this morning and are under way with no problems so far, but then again, we've not had any pitching and rolling. We don't really expect any more fuel system problems.

The summary of our fuel system problems is that the tank had about 1/4 inch of gunk in the bottom, which clogged the fuel pickups. The gunk was thick enough that it didn't get pulled into the filter. Cutting a 5-inch inspection port in the top of the tank was the best thing we've done. We're planning to do the same thing on the starboard tank in the spring.

Here is a useful link about the sources of diesel fuel gunk from Marsh Marine:


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