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Old 23-08-2012, 04:13   #1
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Deteriorating Plasic Fuel Tanks ??

We have a 2003 Beneteau 50 with two 250 liter fuel tanks made of black plastic. We had a number of problems with revs dropping on the engine and poor engine performance because the fuel-pickup was clogged with small shards of plastic from the fuel tank.
We originally thought this was from when we had our Webasto heater installed and the installers using a hole-saw to drill into the tank creating the shavings that clogged up the fuel pickup pipe. The solution I came up with was to remove the tanks, clean them out and then reinstall them ... then I had the fuel pickup changed from having a 3mm or so wide pipe to a 10mm wide pipe that is big enough to suck up the gook into Racor filter instead of it getting stuck in the pipe.
Earlier this year I noticed the engine skipping and losing revs (e.g., max cruising engine speed dropped from 3000 rpm to about 2200). I looked at my Racor filter and trapped in the bowl were a bunch more of the shards of plastic that I had cleaned out of the fuel tanks earlier. After dismantling the Racor filter and cleaning out all the plastic, then replacing the 30 micron filter and the filter on my engine (Yanmar 4JH3-HTE) the problem went away.
My question is ... has anyone else had this problem with the plastic fuel tank and is it something that we should keep an eye on ... perhaps replacing them or changing to a different technology -- e.g., have some aluminum tanks made.
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Old 24-08-2012, 04:49   #2
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Re: Deteriorating Plasic Fuel Tanks ??

Hi,

I have pulled a number of black fuel tanks off of Gemini Catamarans and cleaned them. No evidence of tanks doing this. If they were chards, and you could see them,the the cleaning from the drilling was not good to begin with perhaps. I would let those bits dry and try to see if they are made of the same material as the tank. Perhaps they went into the pickup hoses and into the filter and took a while to get to the filter. It is possible that the hoses for the fuel are failing. And if you pulled them off, it is possible that that hose inner wall, for a small area near the crimp came loose and perhaps that is what you are seeing. Can you determine if this is dried bits of hose? It sounds like you might want to remove the tanks again and clean them. The biggest issue we have had is that tanks that are flat bottomed, will accumulate a very thin layer of water, dirt, and sluge that will not come out until you pull the tanks off the boat, tip them over and look at the dregs in a clean bucket. A seperate polishing system that has a pickup going to the bottom of the tanks which i use to pull the fuel out, pushed to the bottom can't get the sluge off. This is pretty clear when you tip the tank and watch the thin layer slowly slide down the bottom. This thin layer on the bottom of sluge, water, contanimints is what gets strired up right when you need the engine the most, going out an inlet for example. The RPM drops and things start to go bad. The other thing is that the fuel removed may be bad and have emulsified water and other issues and should be disposed of. I have seen this happen when some fuel is purchased in jerry jugs while cruising in the Bahamas, puts it in the locker for storage and 'forgets' about it for a year+ and then goes to use it. Dirt from the fuel, dirty jugs, age and water/growth can then be introduced. This older, perhaps defective fuel, should be disposed of. There are lots of easy ways to give this away and then have good fuel in tanks, but only after they have been pulled and drained, washed out and dried.

Good Luck,
Walt,
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Old 24-08-2012, 05:23   #3
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Re: Deteriorating Plasic Fuel Tanks ??

The short answer is no, you're off target. Polyethylene tanks can resist any solvent chemical you can think of, including some very harsh ones.

The slopy work with the shavings is lamentable. You'll get through it.

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(I've done refinery work (chemical engineer) for 30 years.)
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