Leave empty or not ?

[Nightwatch]

The OP has,er,disappeared!

[ditchcrawler]

31 minutes ago, Nightwatch said:

The OP has,er,disappeared!

She was here only 10hrs ago, not every one checks every half hour,only us sad ones sat at home and not boating

 

[dmr]

58 minutes ago, Nightwatch said:

The OP has,er,disappeared!

Don't let a little detail like that stop an interesting thread, it's a discussion forum, not a question answering service.

.............Dave

[Nightwatch]

37 minutes ago, ditchcrawler said:

She was here only 10hrs ago, not every one checks every half hour,only us sad ones sat at home and not boating

 

Speak for yourself. I'm sat at home and boating, well sometimes boating.

[Tony Brooks]

10 hours ago, Bee said:

I am not totally convinced about the 'condensation in the tank' theory and if you put hundreds of £'s of fuel in there is a chance that it could be contaminated, personally I'd rather take a few gallons of bad fuel out in the spring and change the filters a couple of times.

U agree with this, especially as we have no idea what us going on in the tank now. My experience over the last three years of sucking from the bottom of the tank each spring is that I find very little water BUT I do use Fuelset in the spring/summer (into a tank I know is fairly water free) and M16 Complete in the last fill of autumn.

[Naughty Cal]

We don't worry about whether our tank is full or not over the winter. For the last few winters the boat has been sat ashore with half full tanks for a few months with the diesel heater running using more fuel. We just refill as and when we need to.

This year the boat is staying in the water. The tank is about 3/4 full at the moment. We will refill it when we feel we need to after Christmas.

We change our diesel filters every spring and as yet have not had a problem with either diesel bug or water in the fuel.

I personally think the condensation in the tank thing is a bit over worried about. The largest surfaces on a tank will tend to be the top and bottom surfaces. So unless you keep your tank brimmed constantly one of those surfaces will always be exposed.

[Tony Brooks]

47 minutes ago, Naughty Cal said:

We don't worry about whether our tank is full or not over the winter. For the last few winters the boat has been sat ashore with half full tanks for a few months with the diesel heater running using more fuel. We just refill as and when we need to.

This year the boat is staying in the water. The tank is about 3/4 full at the moment. We will refill it when we feel we need to after Christmas.

We change our diesel filters every spring and as yet have not had a problem with either diesel bug or water in the fuel.

I personally think the condensation in the tank thing is a bit over worried about. The largest surfaces on a tank will tend to be the top and bottom surfaces. So unless you keep your tank brimmed constantly one of those surfaces will always be exposed.

Is your tank steel or GRP? GRP is a worse heat conductor than steel so may well be less prone to condensation.

[Mac of Cygnet]

I've just finished a bottle of M16 Complete.  Well, I didn't quite finish it, as there was something lurking in the bottom of the bottle - not gloopy, just sort of sediment.  Didn't feel that would contribute to my fuel.

[bizzard]

7 minutes ago, Mac of Cygnet said:

I've just finished a bottle of M16 Complete.  Well, I didn't quite finish it, as there was something lurking in the bottom of the bottle - not gloopy, just sort of sediment.  Didn't feel that would contribute to my fuel.

Its a matter of taste really. Perhaps it needed a dash of soda or tonic or ice in it.

[Naughty Cal]

3 hours ago, Tony Brooks said:

Is your tank steel or GRP? GRP is a worse heat conductor than steel so may well be less prone to condensation.

Aluminium.

[Tony Brooks]

That should make any tenancy for condensation worse but your experience tends to mirror mine.

[ditchcrawler]

43 minutes ago, Naughty Cal said:

Aluminium.

That would be inside the boat wouldn't it. My tank is part of the hull so the bottom and 4" of the side is below water and about 15"  on 3 sides of the tank is out side as is the top of the tank. How much air moves in and out of the tank via a half inch vent I don't know but I can't imagine it would be much. So does it make lots of condensation, I don't have a clue.

[Naughty Cal]

7 minutes ago, ditchcrawler said:

That would be inside the boat wouldn't it. My tank is part of the hull so the bottom and 4" of the side is below water and about 15"  on 3 sides of the tank is out side as is the top of the tank. How much air moves in and out of the tank via a half inch vent I don't know but I can't imagine it would be much. So does it make lots of condensation, I don't have a clue.

Yes it is tucked away inside the boat in the engine bay.

[DHutch]

5 hours ago, Naughty Cal said:

I personallythink the condensation in the tank thing is a bit over worried about. The largest surfaces on a tank will tend to be the top and bottom surfaces. So unless you keep your tank brimmed constantly one of those surfaces will always be exposed.

I'm inclined to agree it's over played. However I think it's more the volume of air and the amount the temperature changes which will have the effect.

For condensation to form you need a differential between the air and surface. For it form again, you need to change the air and repeat.

 

Daniel

[ditchcrawler]

13 minutes ago, DHutch said:

I'm inclined to agree it's over played. However I think it's more the volume of air and the amount the temperature changes which will have the effect.

For condensation to form you need a differential between the air and surface. For it form again, you need to change the air and repeat.

 

Daniel

But surly you need to put more moist air in it.  for it to repeat,  once you have condensed the water out  of the air into the bottom of the tank there is nothing to condense a second time

[Tacet]

36 minutes ago, ditchcrawler said:

But surly you need to put more moist air in it.  for it to repeat,  once you have condensed the water out  of the air into the bottom of the tank there is nothing to condense a second time

The idea (and I am with the over-played view) is that the air inside the tank expands and contracts with temperature - and thus refreshes through the breather.   The fuller the tank with fuel, the less air there is expand and contract (air has a lower co-efficient net of expansion than the diesel) which means a reduction in fresh, moist air coming into the tank.

It may have been Bizzard who had the suggestion of putting a balloon over the breather to act as a expansion vessel. 

[ditchcrawler]

35 minutes ago, Tacet said:

The idea (and I am with the over-played view) is that the air inside the tank expands and contracts with temperature - and thus refreshes through the breather.   The fuller the tank with fuel, the less air there is expand and contract (air has a lower co-efficient net of expansion than the diesel) which means a reduction in fresh, moist air coming into the tank.

It may have been Bizzard who had the suggestion of putting a balloon over the breather to act as a expansion vessel. 

so 100 lt of air may contract by as much as a 3 lt in our winter and as its cold it will be supporting less moisture, so how much moister could condense out of that extra lt of air drawn into the tank every time the temperature swings by 10 dec C

[Tacet]

According to this http://hyperphysics.phy-astr.gsu.edu/hbase/Kinetic/watvap.html#c1 the saturated density at 10 degrees is 9.4 g/m3 and at 0 degrees it's 4.85 g/m3

It's probably a lot more complicated than this, but assuming your 3% change is across the same range, it looks as though the maximum additional moisture over 100 cycles (days?) for 100 litres of air in the tank, is 1.68 g.

Which does sound very low - so I have probably gone wrong somewhere.

[cuthound]

3 hours ago, DHutch said:

I'm inclined to agree it's over played. However I think it's more the volume of air and the amount the temperature changes which will have the effect.

For condensation to form you need a differential between the air and surface. For it form again, you need to change the air and repeat.

 

Daniel

I don't think it is much of an issue an issue for small tanks such as those found on canal boats (typically 2-300 litres capacity), but it can be an issue with the large tanks I used to work with (up to 100,000 litres per tank). This is because of the volumes of air introduced when large tanks are approaching empty can contain large volumes of water.

I have seen diesel bug infestations with large, above ground tanks, even when using FAME free fuel.

It is becoming popular with critical standby power installations to build in a fuel polishing facility which cleans the fuel whenever the generators run, rather than use chemicals to prevent diesel bug.

3 hours ago, ditchcrawler said:

But surly you need to put more moist air in it.  for it to repeat,  once you have condensed the water out  of the air into the bottom of the tank there is nothing to condense a second time

More moist air will be introduced through the tank vent pipe, air will expand as the tank warms up, so some will escape and shrink when it cools, drawing in more new air.

Edited December 7, 2017 by cuthound
Clarification

[peterboat]

I have washed my fuel guard filter today it had a black film over nearly all of the mesh. I just wash it in soapy water rinse and refit it. Its a twice a year thing and nowt can be done about it

[Chewbacka]

Something else to think about as the op did say they were thinking of not running the engine for 2 or 3 months is that the engine oil may not protect the bearing surfaces if not circulated say monthly - ie by running the engine.  Just running the engine for a few moments which is enough to circulate the oil is bad, as water is produced when diesel is burnt, and this does need 'boiling off' by running the engine until it is at 'normal' temperature.  

[Nightwatch]

Good valid point.

[JonathonGleeson]

The 'best practice' is always to keep your tank full for the said reasons. However, the cost can always seem a lot as a risk if the fuel is contaminated anyway. But I've not had a problem using that way for 15 years

[ditchcrawler]

27 minutes ago, JonathonGleeson said:

The 'best practice' is always to keep your tank full for the said reasons. However, the cost can always seem a lot as a risk if the fuel is contaminated anyway. But I've not had a problem using that way for 15 years

The only problem I had was someone borrowing about 150 lt, and failing to return it over winter.

 

[JonathonGleeson]

24 minutes ago, ditchcrawler said:

The only problem I had was someone borrowing about 150 lt, and failing to return it over winter.

 

You should ask for it back