Filling the fuel tank over winter - yes or no?

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PetiteFleur

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This layup I'm thinking of not filling the fuel tank as I've done in previous years.
The reasons being:-
newish plastic tank therefore no condensation issues;
tank only 1/4 full so when refilled next year will have fresh diesel in it(white road diesel not red);
fuel regularly dosed with MR 16 additive so no bugs;
modern diesel fuel deteriates with age so fresh diesel in the spring will mix with old;
am fitting a screw-on primary fuel filter to replace the c*** CAV filter which is a pita to change.
Is this ok or am I kidding myself?
 
You will get condensation in a plastic tank (though possibly less than in a metal tank) and the water will collect at the bottom. Whether that will be a problem or not only time will tell. We prefer to leave our (metal) tank full over the winter.
 
If you have filled it in previous years over the winter, why change a system that works? I have never had issues with full metal tanks over the winter, and this year with a new boat that has a plastic tank I shall do the same.
 
After the one day "RYA Terrify Yourself about Diesel" course last year the advice was to fill and dose your tank with Soltron, other additives are available.
 
Surely if the tank air valve is closed the condensation will be only from the air trapped in the tank and therefore only a very limited amount?.
 
Condensation will occur on the inside of a tank when the inside surface temperature of the tank drops to the dew point temperature of the air. With no heat source around the air in the tank will be close to the average daily temperature outside which will often be well below the dew point of the air irrespective of the tank material. Prevention is better than cure so stop water collecting in your tank and you'll prevent diesel bug. Add a biocide and you'll cure the bug but the water will remain and can cause terminal damage to injectors. I have used diesel from a sealed can 5 years old and it was fine. I recommend you leave your tank full over the winter.
 
If it all goes excrement-shaped.....would you rather deal with 5 gallons of buggy diesel.......or 100 gallons......?

Excellent precautions already suggested here....but in addition......it makes sense to me to run the tank levels down somewhat low by the end of the season.....if for no other reason than the quantities of expensive " treatment materials" needed will be considerably less to fix any problem.
 
Chris_Mardon said:
Condensation will occur on the inside of a tank when the inside surface temperature of the tank drops to the dew point temperature of the air. With no heat source around the air in the tank will be close to the average daily temperature outside which will often be well below the dew point of the air irrespective of the tank material. Prevention is better than cure so stop water collecting in your tank and you'll prevent diesel bug. Add a biocide and you'll cure the bug but the water will remain and can cause terminal damage to injectors. I have used diesel from a sealed can 5 years old and it was fine. I recommend you leave your tank full over the winter.
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But the important question is "how much air is there in the tank?" And, "how much water can that amount of air realistically hold?" The answer is not very much. And there's almost no flow of air in and out of the tank, so the risk of condensation is minimal. In more years of boating than I care to admit, I've never found water in my diesel filter/separator.
 
pvb said:
But the important question is "how much air is there in the tank?" And, "how much water can that amount of air realistically hold?" The answer is not very much. And there's almost no flow of air in and out of the tank, so the risk of condensation is minimal. In more years of boating than I care to admit, I've never found water in my diesel filter/separator.
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I have - when I got 'the bug' :blue:

I now keep my tank full over winter, dose with M 16 and a couple of times through the season I use my Pela (vacuum type) oil extractor to draw off a small amount of fuel from the very bottom of the tank.
 
Easticks28 said:
I have - when I got 'the bug' :blue:

I now keep my tank full over winter, dose with M 16 and a couple of times through the season I use my Pela (vacuum type) oil extractor to draw off a small amount of fuel from the very bottom of the tank.
Click to expand...

Yes, I had diesel bug in my old boat, which had a permanently plumbed hand pump to draw fuel from the very bottom of the tank. But I never found water in the separator.
 
pvb said:
But the important question is "how much air is there in the tank?" And, "how much water can that amount of air realistically hold?" The answer is not very much. And there's almost no flow of air in and out of the tank, so the risk of condensation is minimal.
Click to expand...

I'm coming around to this point of view too. The condensation issue is maybe just an urban (or yacht club) myth. I reckon the water found in the tank in the spring was in the diesel in the autumn, which would argue for keeping less not more in the tank over the winter.

Maybe someone with a spare tank could carry out an experiment in their back garden over the winter. Starting with an empty tank and providing the it is watertight, and the only way in is via a breather pipe which can't collect rainwater or dew, I suspect very little atmospheric moisture will condense in the tank.
 
Why bother to fill the tank.Get a swing bin bag, tape a length of hosep[pe to it and fasten the hose to your tank breather.When the air expands in the fuel tank it goes into the plastic bag so that the tank is using the same air all the time, so no condensation
 
lpdsn said:
I'm coming around to this point of view too. The condensation issue is maybe just an urban (or yacht club) myth. I reckon the water found in the tank in the spring was in the diesel in the autumn, which would argue for keeping less not more in the tank over the winter.

Maybe someone with a spare tank could carry out an experiment in their back garden over the winter. Starting with an empty tank and providing the it is watertight, and the only way in is via a breather pipe which can't collect rainwater or dew, I suspect very little atmospheric moisture will condense in the tank.
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Yes but.
With an absolutely empty tank, any water which did collect from condensation, could equally well evaporate.
With a tank with even a small amount of diesel in it, the condensed water is trapped under the diesel.
 
NormanS said:
Yes but.
With an absolutely empty tank, any water which did collect from condensation, could equally well evaporate.
With a tank with even a small amount of diesel in it, the condensed water is trapped under the diesel.
Click to expand...

So put a thin layer of diesel in the test tank.

Pete
 
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