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Old 13 November 2014, 15:02   #11
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I put mine away with whatever is in the tank and slop a bit of stabiliser in. I top up with fresh for the first run of the new season, after each of the first 2/3 runs, I empty the contents of the fuel/water separator into a jamjar to check whether it's pulled any water out.
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Old 13 November 2014, 17:46   #12
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Modern fuel contains minimum 5% ethanol. This precipitates water when left to stand for a decent length of time, so you end up with a layer of water at the bottom of the fuel tank.
Pretty sure a precipitate needs to be solid.

Suspect what is actually happening is the water dissolves in the ethanol, then over time the ethanol evaporates leaving the ethanol behind. So those of you who add some fresh fuel will add some new ethanol which redissolves the water in the ethanol and then the water is 'burned' off in the engine...

Tricky balancing act. Leave less fuel in the tank you can add more fresh and disperse the crap in a bigger volume so burn the crap more gradually. But big air space can have more moisture in it, which in winter can then condense. Conversely fill it to the brim, no airspace for water vapour and no airspace for the alcohol to evaporate into. But if there is water present there is no room to add fresh fuel to remix it in...

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The water will also swell and distort nylon tanks (search online for Ducati fuel tank swelling) as nylon absorbs water.
Personally, I would drain it if at all possible.
But do most people not have HDPE or MDPE polyethylene tanks rather than nylon? Pretty sure the water content on the outside of my fuel tanks is far far higher than the inside...
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Old 14 November 2014, 07:18   #13
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I used to top the tank up full and put a bit of stabiliser in. Don't bother now. Just top off the tank after winter and leave the cap off when she's in the shed.

No problems so far.
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Old 14 November 2014, 16:45   #14
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I used to top the tank up full and put a bit of stabiliser in. Don't bother now. Just top off the tank after winter and leave the cap off when she's in the shed.
Not only do you allow more air transfer, which means more water, into the tank by leaving the cap off, but the fuel can evaporate faster leaving the parts you don't want behind. I would highly recommend switching back to what you used to do. Not like it is hard to fill a tank, nor is it expensive to put a fuel additive in.
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Old 16 November 2014, 18:12   #15
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Pretty sure a precipitate needs to be solid.
OK!
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Suspect what is actually happening is the water dissolves in the ethanol, then over time the ethanol evaporates leaving the ethanol behind. So those of you who add some fresh fuel will add some new ethanol which redissolves the water in the ethanol and then the water is 'burned' off in the engine...
Almost. Water is absorbed by the ethanol, which then separates (not precipitates ) the water out from the fuel to form a layer of water/ethanol mix at the bottom of the tank - this is called phase separation and (in theory) can be reversed by adding ethanol to the mix. You need to know how much water is in there in order to add the correct amount of 'corrective' ethanol.
The separated fuel also has a lower octane rating which can cause running problems.
Quote:

Tricky balancing act. Leave less fuel in the tank you can add more fresh and disperse the crap in a bigger volume so burn the crap more gradually. But big air space can have more moisture in it, which in winter can then condense. Conversely fill it to the brim, no airspace for water vapour and no airspace for the alcohol to evaporate into. But if there is water present there is no room to add fresh fuel to remix it in...


But do most people not have HDPE or MDPE polyethylene tanks rather than nylon? Pretty sure the water content on the outside of my fuel tanks is far far higher than the inside...
I've no idea, I was just stating that it causes problems with nylon fuel tanks which are relatively common on road vehicles.

Given the choice, I'd still drain off any fuel if the boat was going to stand over winter.
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Old 17 November 2014, 03:20   #16
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I failed chemistry at school ;-)
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Old 17 November 2014, 03:36   #17
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This is all more or less true if the assumption about alcohol presence in modern fuel is correct.
I am not so sure about that, it probably depends on the country and/or fuel brand.
In most European countries there can be up to 5% alcohol in gasoline, but the actual content may be much lower or even zero.
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Old 17 November 2014, 13:28   #18
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Over here its typically 10% ethanol, although you can with effort you can find ethanol free gasoline.

If I were leaving it for 4 or 5 months I'd use stabilizer. Less than that I have never had an issue. It will likely to hard starting at first but that's pretty much a given regardless of the fuel inside. If you have carbs I would drain them. The fuel in the tank is typically "good enough", but the fuel in the carbs tends to evaporate more and leaves a gummy mess.

Best choice of all is to use the boat over the winter
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Old 18 November 2014, 04:25   #19
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Over here its typically 10% ethanol, although you can with effort you can find ethanol free gasoline.
That's bad. The only stuff with 10% ethanol here is cheap wine.

Water in fuel seems to be a serious problem, poor starting, corrosion and gasket damage.
Did anybody try placing a bag of silica gel in the tank filler? A tank cap with a cavity for it might be a useful gadget.
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Old 18 November 2014, 04:30   #20
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some winters have filled tank with the intention of using the boat - but not.

Some winters left the tank half full.

Never had any problems in the spring either way.
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