Condensation in fuel tank

ianc1200

ianc1200

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Was on the Broads last weekend with my Cornish Crabber. The engine faded and cut out on leaving moorings above Wroxham. When I looked into the cause I had at least 2 litres of water in my tank, fuel filter etc. Spent a happy day emptying tank and bleeding through etc. However the whole engine installation is less than 4 years old, including new tank. It's a Vetus 25L translucent tank, and my question is, for three winters (where I foolishly left half empty) would condensation have resulted in 2 (if not more) litres of water?
 
Thats a lot of water to get from condesation.I suspect you have either been sold duff fuel with water in it or you have a leak from the deck or filler pipe into the tank.
 
Biggles Wader said:
Thats a lot of water to get from condesation.I suspect you have either been sold duff fuel with water in it or you have a leak from the deck or filler pipe into the tank.
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+1

We fitted a new fuel tank in Kindred Spirit, filling it initially with jerrycans of white. After the first fill-up from a fuel barge, we had loads of water, sludge, and rust flakes in the bottom. The next week the fuel barge was off-station to be refilled. We obviously got the dregs.

Bad fill, or leaky filler cap. Check the O-ring in the latter.

Pete
 
Biggles Wader said:
Thats a lot of water to get from condesation.I suspect you have either been sold duff fuel with water in it or you have a leak from the deck or filler pipe into the tank.
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+1 Agree Only last month I spent four days getting my port tank out to completely clean it after getting water in via a faulty deck fuel filler cap.
One tip is to always add some grease around the filler cap threads.
 
That needs to be well filtered and treated with Marine 16 for bug before going anywhere near your fuel tank.About half of it should be suitable for use,the rest for starting your bonfire.:)
 
It does sound like water in the fuel but if you have a fuel return pipe the hot fuel going into a cold tank will cause condensation. Water and dirt in the fuel was endemic in the Caribbean so we used a filter to remove both. You will find it here: https://www.amazon.co.uk/Fuel-Funnel-Filter-Separator-Removes/dp/B000SOKE5E the one with the green coloured filter. Light aircraft use that too.
 
ianc1200 said:
Fuel has been in those bottles overnight.

Where can I dispose of it?
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I had some in a similar state, I left it in plastic bottles behind the shed and it settled out in the end.
I left it for a few weeks, but don't know how long it took.
The bright stuff went through a filter and into the tank.
The 'not quite' stuff is dead handy for things like cleaning motorbike chains.
The dregs went into a waste oil vat at the council dump, along with some sump oil.
 
AngusMcDoon said:
Useful myth buster...

http://www.yachtsurvey.com/myth_of_condensation_in_fuel_tanks.htm
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That analysis seems flawed to me in that it doesn't take any account of diurnal temperature variation causing partial air exchange daily through the vent.
However my co-owner who is ex oil industry also doubts the importance of condensation. His view is that diesel fuel is normally saturated or close to it when it leaves the refinery even before it gets into possibly dodgy tanks at the retailer! So the conclusion is broadly the same, the water comes in with the fuel.
 
Plevier said:
That analysis seems flawed to me in that it doesn't take any account of diurnal temperature variation causing partial air exchange daily through the vent.
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I have a 50 litre fuel tank. If the ambient temperature dropped from +10oC (283K) to -10oC (263K), the air in an empty tank would fall from 50 litres to (263/283 x 50 litres) = 46.5 litres, so 3.5 litres would be sucked in.

At 10oC, the maximum moisture content of air[1] is 9.39 g/m3, so those 3.5 litres could carry in at most 32 mg of water. If this happened every day for 180 days of layup, it would produce 6 g (ie 6 cc) of water in my tank.

In practice my tank is not empty, the air is not usually saturated and the temperature often does not get as high as 10o. I'd be surprised if I got 1 cc of condensation in the fuel tank over winter.

[1] http://www.engineeringtoolbox.com/maximum-moisture-content-air-d_1403.html
 
We've discussed fuel tank condensation many times on the Forum. The result is always the same ..... it's an urban myth.

Just forget about it and try to focus on how the water is really finding it's way into your tank because it's not condensation. :)

Richard
 
RichardS said:
We've discussed fuel tank condensation many times on the Forum. The result is always the same ..... it's an urban myth.

Just forget about it and try to focus on how the water is really finding it's way into your tank because it's not condensation. :)

Richard
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So you know better than the CAA and FAA? Checking for water in tanks is part of DI on all aircraft and there are various circulars advising operators to leave tanks full to help avoid the problem. I don't think there's much difference between aircraft and uninsulated tanks in boats and shore storage.
 
GrahamM376 said:
So you know better than the CAA and FAA? Checking for water in tanks is part of DI on all aircraft and there are various circulars advising operators to leave tanks full to help avoid the problem. I don't think there's much difference between aircraft and uninsulated tanks in boats and shore storage.
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There is a huge difference with plane tanks.
They fly!
Hence much greater temperature and pressure changes.
 
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