Keeping diesel tank filled over winter

I always tried to leave my tanks full over winter but because of low useage in the last couple of years I can't be bothered to make a special trip to fill up so they will sit with what is in them!
I think I am developing a NFI attitude. Sort out any problems as they arise.
 
You have a choice; fill the tank to near the brim - let's not go overboard about having fuel spilling out of the tank - mainly full does the job.

Alternatively, and to serve the main purpose of keeping moisture out of the tank, how about taping a plastic cup or covering over the tank ventilator fixture to prevent air circulating into the tank over the winter.

Otherwise seems good practice, one I've always followed, and to date no water problems in the following season.

Some owners get a little edgy about the fuel ageing - this year is one of those problem seasons - but I've not found such ageing to be a problem. No bad thing to give the tank a dosing of one of the diesel fuel pepper-uppers. I can recommend it - mostly for reassurance than for some magical additional performance.

PWG
 
RichardS said:
It's a side issue .... but do some cats really have the fuel tanks in the bridgedeck? I would have thought that carrying all that weight so high is rather counter-productive when they could be easily mounted down in the hulls near the engines.
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My elderly Prout had a single engine with outdrive leg on the bridgedeck and fuel tank under the cockpit. It kept all the smelly stuff well away from the accomodation. So yes, some cats do have fuel tanks above the waterline.
 
Hoolie said:
My experience is similar to yours. For reasons I won't go into here (it's a long story) our boat was out of the water for nearly two years. Prior to going back in I ran the engine to check and it started right away on what must have been 3 year old diesel in a half-empty tank.
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I've just got to the end of a tank I last filled up in 2014. No ill effects.
This time.due to new legislation, I've had to put in road diesel but also, due to the same legislation, I can't have any trace of green diesel after the end of 2020, so I'm only putting in one 20 litre drum-full at a time, in order to try to get rid of the green dye without having traces of it lingering in in a full tank for potentially, years.
 
When bought our boat at the end of last year it had approx 120L (in 190L s/s tank) of diesel from at least 2014 or older. Pumped it out over a few months and ran the van on it for free - luckily before pump diesel prices fell!

No sign of water (nothing in filter bowl and nothing settled out in the 25L jerry cans). The last 5L was a bit suspect and that was all that needed recycling.

Not sure I’d have run the engine on it (300hr Beta 50 so still a bit ‘precious’). But it certainly wasn’t saturated with moisture, unless it was so emulsified to deceive my eyes, the racor, and the van’s EFI Diesel engine! ??
 
Plum said:
Agree, my 40 years of experience, I have never had water in a tank through not filling it over winter and I have done the calculations that show the amount you could get is insignificant. I am, however, meticulous about a good seal on the filler.

www.solocoastalsailing.co.uk
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Experince with silcia gel filters is that 2-5 ounces per year (12 months) is typical. Less than1/3 of that would be absorbed by the fuel. Remember, deisel can absorb water without actual condensation, and that condensation will fall through the diesel and not evaporate during the day. It tends to be a one-way thing. So only an ounce or so in the off season. With gasoline, particularly E10, the rates are as much as 10 times higher, since breathing is much greater. There is also evaporation.
 
pvb said:
Your car is outside, and prone to condensation.

The fuel in your tank is inside. With changes in air pressure, some airflow might occur in the vent pipe, potentially bringing moist air in. But the subsequent increase in air pressure in the tank would drive air back up the vent pipe. On balance, unless the tank is huge and empty, I reckon the same air will mainly flow back and forth in the vent pipe. So I don't think much moisture is going to find its way in.
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Indeed, that.
The conclusion was (wording may differ) no matter what boat, tank or weather, condensation is not the cause of water in the fuel.
 
This thread should be put in the box labelled 'old seawives tales' along with the one about engine intake scoops not facing forward!
 
julianmingham said:
Thanks for all the interesting responses, my conclusion is to leave it half full. Also to ensure that the filler and/or vent is well sealed.
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I think you will find that the tank will breathewith fluctuations in temperature and atmospheric pressure more than pvb is suggesting

If you have a tank with a capacity of around 200 litres it will contain 100 litres of air when half full
A pressure fluctuation of 10 mb or a temperature fluctuation of slightly less than 3°C will result in the tank drawing in or expelling a 1 litre of air.
pvb suggests that the volume change will be taken up by the volume of the tank vent hose . However 2 metres ( a likely length given the size of the boat) of 16 mm bore hose has an internal volume of less than half of that.

If the temperature falls below the dewpoint of the air in the tank condensation will occur. Although it is impossible to make ant sensible estimate of the volume of water condensing the effect is cumulative

To prevent this you will have to tightly seal the tank vent ( or fill the tank)
 
I had thought of plumbing a valve into my vent hose for easy sealing of the breather...with a note on the engine key to remember to open it ;-)
 
ashtead said:
Would using white garage diesel be better for the overwintering than the over priced red stuff? It seems it’s cheaper ar ASDA than many marine places?
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Only if you have cleaned the tanks and pipes before running lots of white through the system and then using in the car when not needed.
 
VicS said:
I think you will find that the tank will breathewith fluctuations in temperature and atmospheric pressure more than pvb is suggesting

If you have a tank with a capacity of around 200 litres it will contain 100 litres of air when half full
A pressure fluctuation of 10 mb or a temperature fluctuation of slightly less than 3°C will result in the tank drawing in or expelling a 1 litre of air.
pvb suggests that the volume change will be taken up by the volume of the tank vent hose . However 2 metres ( a likely length given the size of the boat) of 16 mm bore hose has an internal volume of less than half of that.

If the temperature falls below the dewpoint of the air in the tank condensation will occur. Although it is impossible to make ant sensible estimate of the volume of water condensing the effect is cumulative

To prevent this you will have to tightly seal the tank vent ( or fill the tank)
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But the water content of that litre of air is really very small, and not much of that will condense for a typical change in temperature.
The water content of 100% humid air at 20degC is only 17g per cubic metre.
You have to have big changes in temperature and pressure, combined with high humidity, to conjure up a lot of water.
As the vapour pressure of water increases more than linearly with temperature, it's going to be less of problem than it is in Summer.
 
VicS said:
If you have a tank with a capacity of around 200 litres it will contain 100 litres of air when half full
A pressure fluctuation of 10 mb or a temperature fluctuation of slightly less than 3°C will result in the tank drawing in or expelling a 1 litre of air.
pvb suggests that the volume change will be taken up by the volume of the tank vent hose . However 2 metres ( a likely length given the size of the boat) of 16 mm bore hose has an internal volume of less than half of that.
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You've used the size of the boat to predict a possible length of the vent pipe, and I'd say your guess of 2 metres is on the low side, bearing in mind the need for swan-neck looping. The OP has a Rival 34. Online brokers' details suggest the Rival 34 has either a 90 litre or a 110 litre fuel tank - half the size you've chosen to use for your calculations! If you use the correct figure for the tank capacity, and a more realistic vent pipe length, my theory makes sense.
 
ashtead said:
Would using white garage diesel be better for the overwintering than the over priced red stuff? It seems it’s cheaper ar ASDA than many marine places?
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I know some folks had trouble with asda petrol in certain cars. Maybe it was a bad batch.
Not all fuel is the same !
If something works for you, stay with it........
 
pvb said:
You've used the size of the boat to predict a possible length of the vent pipe, and I'd say your guess of 2 metres is on the low side, bearing in mind the need for swan-neck looping. The OP has a Rival 34. Online brokers' details suggest the Rival 34 has either a 90 litre or a 110 litre fuel tank - half the size you've chosen to use for your calculations! If you use the correct figure for the tank capacity, and a more realistic vent pipe length, my theory makes sense.
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I have been mislead by the fact that he calls it a "Westerly yacht called Golden Eye" in his blog Doesn't look like a Rival either

Somehow I'd deduced that he had an Oceanlord
 
VicS said:
I have been mislead by the fact that he calls it a "Westerly yacht called Golden Eye" in his blog Doesn't look like a Rival either

Somehow I'd deduced that he had an Oceanlord
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In that case, I've been misled by his profile, which says he has a Rival 34. And he doesn't list a blog in his profile, so where did you find that?
 
pvb said:
In that case, I've been misled by his profile, which says he has a Rival 34. And he doesn't list a blog in his profile, so where did you find that?
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It took me a while to retrace my steps
He signs off one post with a reference to Elaine and Julian's Sailing Adventures Sailing adventures of a Westerly yacht called Golden Eye
In another ( last year I think) he refers to an Oceanlord.
I assume Golden eye is the Oceanlord
 
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