Topping up the fuel tank for winter

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richardabeattie

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The standard advice has always been to lay up for the winter with full tanks - to reduce the air space where condensation forms and thus the bug. But now we are told that with blended fuel containing bio diesel it's better to leave the tank more or less empty for the winter because bio fuel is hygroscopic and attracts water - plus the new bio blends go stale almost as fast as petrol does. So which way should we jump?
 
drain the tank of diesel, close the drain tap, close off the the breather pipe, and fill the tank with nitrogen. No air can get in, so no water can get in.
 
sarabande said:
drain the tank of diesel, close the drain tap, close off the the breather pipe, and fill the tank with nitrogen. No air can get in, so no water can get in.
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I wonder about a non-return valve on the breather, like motorbikes have.
But the tank etc would have to withstand pressure as atmospheric pressure and temperature changes.
If the breather is a small hole, I doubt much water enters in reality.
 
I expect that over the layup period, an empty /partly empty diesel tank will exchange internal air with the external atmosphere quite a lot. It's not only temperature causing expansion and contraction of the air, but any change in relative humidity will also be transferred to the free air inside the tank (Boyle's law, I think ?).

An empty, sealed, tank is the safest way for a good start next season.
 
I think it's a myth that condensation forms in the tank, and so a waste of time to fill up.

But it is essential not to have water in the tank, so rather than fill up, make sure that there is no water by opening the lid and peering in (and, if need be, sucking any water out).
 
jdc said:
I think it's a myth that condensation forms in the tank, and so a waste of time to fill up.

But it is essential not to have water in the tank, so rather than fill up, make sure that there is no water by opening the lid and peering in (and, if need be, sucking any water out).
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I have three large plastic tanks for red, white and heating oil. The tanks are about 1200l each, and stand outside. I know from direct experience that water gets inside each tank (there are traps on the outflow line). The only way in is from atmospheric humidity.

Peering in is not an option for most people with tanks on board. Prevention is key; response to a water initiated bug or degradation is expensive, and can be easily mitigated by standard over-winter procedures, e.g. filling, and/or isolating to prevent water vapour getting into the tank.
 
jdc said:
I think it's a myth that condensation forms in the tank, and so a waste of time to fill up.

But it is essential not to have water in the tank, so rather than fill up, make sure that there is no water by opening the lid and peering in (and, if need be, sucking any water out).
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How would you know? The water,if any, will be covered by diesel.
 
There was a suggestion many years ago in a magazine to put a balloon over the breather. I have never done it but it sounds sensible, and would cut off access to moisture.
 
jdc said:
I think it's a myth that condensation forms in the tank, and so a waste of time to fill up.

But it is essential not to have water in the tank, so rather than fill up, make sure that there is no water by opening the lid and peering in (and, if need be, sucking any water out).
Click to expand...

You're right. It is a myth. The water fairy brings the condensation. Trouble is, she doesn't know she's a myth.

As to your tank inspection...you make it sound like peering into a wheelie bin. Most tanks don't lend themselves to this at all, nor to a simple means of removing water (although they should).
 
macd said:
You're right. It is a myth. The water fairy brings the condensation. Trouble is, she doesn't know she's a myth.

As to your tank inspection...you make it sound like peering into a wheelie bin. Most tanks don't lend themselves to this at all, nor to a simple means of removing water (although they should).
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My tanks do lend themselves to simply peering in: not quite as simple as a wheelie-bin, one does need a 13 mm spanner, but trivial nonetheless. This is why I know that, in the damp of a Cornish winter, we never have got any water in the tank despite me never topping up before haul-out and storage ashore.

It amazes me that we all change oil and winterise the engines, and wash ropes and valet sails and check stern-glands etc etc, but the whole yachting industry, including the press, are happy that we don't bother with making sure the fuel tank is clean and dry.

Not to do this is incomplete servicing of the engine. Instead common 'advice' is to add some biocide and hope for the best. That's like never cleaning the kitchen work-tops, just occasionally spraying some Dettol around; it may reduce the chance of food poisoning, but would you want to eat at that restaurant?
 
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jdc said:
My tanks do lend themselves to simply peering in: not quite as simple as a wheelie-bin, one does need a 13 mm spanner, but trivial nonetheless. This is why I know that, in the damp of a Cornish winter, we never have got any water in the tank despite me never topping up before haul-out and storage ashore.

It amazes me that we all change oil and winterise the engines, and wash ropes and valet sails and check stern-glands etc etc, but the whole yachting industry, including the press, are happy that we don't bother with making sure the fuel tank is clean and dry.

Not to do this is incomplete servicing of the engine. Instead common 'advice' is to add some biocide and hope for the best. That's like never cleaning the kitchen work-tops, just occasionally spraying some Dettol around; it may reduce the chance of food poisoning, but would you want to eat at that restaurant?
Click to expand...

I think that is a bit unfair? Adding Biocide is a perfectly good preventative measure and widely used commercially. It is not, "Hoping for the best." I guess it all comes down to the size of your tanks. Most would not find throwing away the dregs of a small tank, perhaps using it elsewhere but with bigger tanks on leisure craft now you might find it difficult to remove a large amount of fuel and the cost is another factor.
I have never heard of diesel or Marine Gas Oil to give it its proper name going bad?
 
Boating since 1968 I've drained a separator bowl once or twice over the years, but not more than spoonful of water or so.
Never had an issue with water or contamination of fuel (petrol and diesel).

Always keep tank full and since the introduction of 'green' also use anti bug additive (even claims properties against water issues + a number of wonderful side effects).
 
Good, well designed tanks have a small bottom area, and also are fitted with dirt sumps with drain valves. Sadly, very few modern tanks seem to be like that. Mine are.:D

I fill my tanks for the winter, have never used biofuel, have never used any additives, and have never had any trouble. Hope I'm not asking for trouble now.
 
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