Keeping diesel tank filled over winter

J

julianmingham

Well-Known Member
Joined
2 Sep 2002
Messages
72
Location
London
Visit site
Like many UK based sailors I have always followed the traditional advice and kept the diesel tank full over winter. But I’m now in Portugal (on the Algarve) and wondering if I still need to keep the diesel full over winter ?

I sailed my boat from the U.K. to the Algarve last year, arriving in September, and filled the diesel tank shortly after I got here. That same tank of diesel is now half full.

on the ‘for’ argument I do get condensation inside the boat in the winter in the Algarve so on that basis there may well also be condensation inside the diesel tank.

on the ‘against’ argument Covid-19 is not going away time soon and I’m reluctant to put diesel in the tank that may sit there for a really long time.
 
The advice was always poor.
You're better off having half a tank of suspect diesel in the spring rather than a full one.
 
Add a silica gel vent filter (H2OUT and others) and you won't have to worry about condensation. Yes, there is always some water absorption. I'm an API-licenced tank inspector, and I've yet to see a diesel tank that did not have dew on the underside of the roof in the morning. Whether it is enough to form a free layer is variable (generally not), but even dissolved water can add to corrosion, sludge formation, and bio-growth. A vent filter is an easy solution. Change the gel at 5-7 years. You can also cook the gel out and reuse it, probably for decades.

Age is never good. Diesel is not perfectly stable and you change your oil every year, right? Try to run the engine enough to get through the tank every year.
 
I do wonder about the amount of condensation that will occur in a part-full yacht diesel tank over winter, given that the only access to the air is a longish and very small diameter vent pipe. Particularly if it is a plastic tank, that gives some heat insulation. May be different with metal tanks. Despite this I do fill tank before winter.

I suspect that most of the water I find every few years in my 130 litre plastic tank comes in with the red diesel fuel being pumped in. Certainly some muck does: the inside of the tank was totally clean this spring, next time I take off the access hatch (not in a rush to do this) there will probably be some black water and some gritty muck that is unlikely to be a diesel bug product. I have had black slime before I used Marine 16.
 
thinwater said:
Age is never good. Diesel is not perfectly stable and you change your oil every year, right? Try to run the engine enough to get through the tank every year.
Click to expand...

I filled my tank and added biocide at the end of 2015, in the Azores. For various reasons have only been able to run the engine three or four times a year for not much longer than it takes to get up to working temperature. Same fuel is still in the tank and the engine starts first go each time and runs smoothly. On the same theme when I bought the boat it had been laid up ashore for two years, and the white diesel had been in the tank even longer. Once we launched the engine started and ran without problem.

My experiences leaves me wondering what the problems are with using 'old' diesel, other than external contamination.
 
I'm usually afloat in the tropics of Plymouth, but when the boat is out of the water every third winter the fuel is removed from the boat and used in the car - I use white diesel before every starts panicking. The tank and fuel lines are then cleaned and fresh fuel added before I get splashed.
 
There was a very lengthy thread on this topic on the dutch sailing forum.
After a lot of calculations the conclusion was that condensation is not a problem, either full, half full or empty.

If there is a problem with water it comes from somewhere else, usually the filler in some shape or form.

Age has become more of a problem with diesel, the higher precentages of biological components easily deteriorate and create a mess.
In this respect an empty tank is better.
I switched to GTL (gas to liquid diesel) in 2014 and this year to xtl/hvo100 which is more or less the same stuff.
HVO stands for Hydrogenated vegetable oil which is not to be confused with "vegetable oil" that older diesels can run on.

GTL and XTL burn cleaner and do not have biological components mixed in.
Burns more cleanly and should water be present gives less problems.
But in the presence of water will/may not be totally free from problems.
 
I'm in the Algarve and have always filled it up before winter out of habit. Never had a condensation issue. I'm not going to change a winning method. For most people on sailing boats it won't be mega bucks to fill up.
I'm not sure what meaningful calculations could have been carried out by the Dutch forums. Do they know temperatures, dew points, tank sizes, tank materials, atmospheric vent sizes etc etc of any given situation.
You want to see my car every morning in winter out here. Dripping with condensation most days first thing in the morning.
Nah - not convinced, I'll be filling up as always.
 
greeny said:
I'm not sure what meaningful calculations could have been carried out by the Dutch forums. Do they know temperatures, dew points, tank sizes, tank materials, atmospheric vent sizes etc etc of any given situation.
You want to see my car every morning in winter out here. Dripping with condensation most days first thing in the morning.
Click to expand...

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.
 
srm said:
My experiences leaves me wondering what the problems are with using 'old' diesel, other than external contamination.
Click to expand...
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.
 
Most people who give an opinion on this stuff believe that petrol goes off more quickly than diesel. We bought an old Landy that has stood for at least 5 years with a couple of gallons in the bottom of the tank. Put a new battery on her and she started and ran like a dream.

Richard
 
It's very difficult to make comparisons between boats.

Wind. If the breeze blow across the vent that makes a difference.

Location. If the tank is in the bilge that can help, but if it keeps the tank cool when the air is warm, it only increases convection (there can be 2-way flow) in the vent. Water temperature is a huge factor. Bridge deck tanks (multihulls) and deck tanks (power boats) are different.

Accesories. Any restriction in the vent, such as a silica gel filter or Parker LifeGuard will greatly reduce convection.

Diesel quality. Some is very, very stable and will keep in a glass jar for years. Some is not and will form sludge within 6 months. Some has bugs in it, some does not.

Fuel system materials. Metals tend to make diesel less stable (catalysis). Copper alloys and zinc are particular problems (ASTM and ISO ban them from standby generator fuel systems, arn't most boats a lot like stand-by generators?).
 
thinwater said:
Location. If the tank is in the bilge that can help, but if it keeps the tank cool when the air is warm, it only increases convection (there can be 2-way flow) in the vent. Water temperature is a huge factor. Bridge deck tanks (multihulls) and deck tanks (power boats) are different.
Click to expand...
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.

Richard
 
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.
Click to expand...
You're probably correct but as I said, I'll stick with the successful system that works for me. No downside doing that.
 
pvb said:
Certainly, if you look at the physics involved. I'm not convinced that condensation in the tank is a serious issue in winter.
Click to expand...
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
 
You must log in or register to reply here.

Share this page

Top