Fill my diesel tank for the winter or not?

[garvellachs]

Conventional wisdom says: fill the diesel tank so that there is no air at the top thus preventing condensation forming in the tank over the winter on the hard. However, I know my 100 litre plastic tank (which is 3/4 full) has plenty of road diesel in it currently - it's not easy sometimes to get the preferred marine diesel when cruising; and I know that road diesel doesn't last well when left unused and is more prone to the bug.

So the question is: should I fill the tank up, or empty it out, or just leave it as it is?

Then come the sums. I find on the web that a litre of air at 20 deg C can hold up to .017 ml of water vapour (and about half that at 10 deg C). So the empty quarter of my tank has maybe 0.2 or 0.3 or 0.4 ml of water vapour in it depending on the temperature and humidity. I have an enzyme treatment in the fuel to remove water anyway. If I put a bit of rag in the breather to stop the air being changed much is there really a problem to worry about here? Any fuel specialists around here?

 

[knuterikt]

Read this article before deciding http://www.pbase.com/mainecruising/fuel_tankt_condensation

 

[garvellachs]

Interesting - thanks. The article suggests empty is good - but it doesn't really address the reality of 3/4 full. There's a comment at the bottom suggesting the fuel traps any condensed water, stopping it from evaporating again. That makes sense I think?

 

[tillergirl]

Testing for condensation in an empty and bone dry tank doesn't really help with the half full question - for which I would like to know the answer. I drained my tank last winter to clean it and left it empty and dry all winter and had no condensation.

 

[sailorman]

Mine is kept topped-up in the vain hope of getting a sail or two in over the winter

 

[Caer Urfa]

Conventional wisdom says: fill the diesel tank so that there is no air at the top thus preventing condensation forming in the tank over the winter on the hard. However, I know my 100 litre plastic tank (which is 3/4 full) has plenty of road diesel in it currently - it's not easy sometimes to get the preferred marine diesel when cruising; and I know that road diesel doesn't last well when left unused and is more prone to the bug.

So the question is: should I fill the tank up, or empty it out, or just leave it as it is?

Then come the sums. I find on the web that a litre of air at 20 deg C can hold up to .017 ml of water vapour (and about half that at 10 deg C). So the empty quarter of my tank has maybe 0.2 or 0.3 or 0.4 ml of water vapour in it depending on the temperature and humidity. I have an enzyme treatment in the fuel to remove water anyway. If I put a bit of rag in the breather to stop the air being changed much is there really a problem to worry about here? Any fuel specialists around here?

Always keep my tanks filled in the winter to prevent condensation without any trouble and never put any additives in it, forget all this so called winterisation of engines other than antifreeze best way to keep an engine in winter is to use it all year round!


Mike

 

[l'escargot]

I think the tradition of filling tanks to stop condensation is out there with the idea of lifting boats onto a cold, wet quay in the English winter in order to dry them. I've never done either with any of my boats and haven't suffered any detriment from not doing so.

 

[corinthmistral]

I keep mine full, also of road diesel and I have never had a problem using the fuel in the spring. I appreciate that modern fuel supposedly doesn't last well but the last few seasons I have had no problem with fuel that has sat for 5 or 6 months. One year I left the tank half full and regretted it in the spring when it was choked full of diesel bug. Albeit that was a few years ago and was predominantly red diesel from the marina which doesn't churn it's tanks very often. (And I added half a bottle of Marine16 and it fixed t without even having to drain the tank - amazing stuff. No link etc, just a very satisfied customer.) so personally I would keep the tank full as there is more risk of condensation and diesel bug than there is of having a problem with using 6 month old white diesel.