To Top Up the Diesel Tank or Not?

[Gypsyjoss]

Hi Guys
Faced with the traditional winterising job of topping up the fuel tank which is a P in the A, I decided to consult the experts, in this case Hydra International Ltd who manufacture fuel additives and supplied me with my bottle of Anti-Bacterial Additive.
The engineer I spoke to did NOT recommend topping up the tank, and indeed to have as little as possible in the tank for the winter period because modern diesel fuels aren't stable for much longer than a month!
He accepts that filling the tank up reduces condensation but said that in the UK, condensation is not a big problem and what there is can be easily drained off at the primary fuel filter.
Comments?
Cheers!
Pete

 

[Old Bumbulum]

modern diesel fuels aren't stable for much longer than a month

I'm sure most of us here would like to know more about this extraordinary statement. If it is really true it turns our fuel hygiene habits on their head.

 

[lw395]

Check the tank in spring and get fresh diesel then.
A lot of yacht tanks don't draw from the very bottom, so there is often water in there which doesn't make it to the filter until things get shaken up. Know what's going on in your boat.
Exactly how long you can usefully store diesel is debatable, but there is no upside to keeping it over winter, particularly in an unsealed yacht tank. Fuel companies do not recommend storing it for months.
The advice to keep tanks full over winter was never great, except perhaps with plain steel tanks. With 20th century diesel it's a bad idea.

 

[Mistroma]

I had also heard about diesel only being stable for a month. I have always topped up the tank and continued the habit. However, I have noticed a steady increase in contamination since leaving the UK in 2012. I filter almost all fuel and rarely fill the tank directly from a pump. The tank is opened twice a year, after a period to allow settling, and fuel pumped from bottom of the tank. Fuel is double-dosed with Marine16 at start and end of season.

The following points might be of interest:

1) Bottom of the tank was spotless in 2012. About 10mls of black material removed in 2013. Contamination increased each year and I removed about 250mls in Sardinia, 2016. About 1 litre and 2 litres cloudy material removed in 2017, 2018 respectively (Greece).

2) I have never seen any water when draining the water sep. unit. Not too surprising as fuel is mostly filtered and tank filler seal is in good order.

3) I have found contamination in fuel cans for first time in 2018. The fuel looked fine when purchased (translucent tanks, stored in dark). I spotted fine brown cloudy liquid when using after 1-2 months. I'd rarely, if ever, seen anything in the Mr Filter before reaching Greece.

Next year I'll try to have the tank close to empty over winter.

 

[vyv_cox]

The instability is a result of the addition of FAME, bio-diesel. It has been the case that the limit was 6% but I read recently that this will increase. It is very difficult for us to know whether FAME has been added to fuel but some marinas in UK supply fuel that is guaranteed FAME free. Elsewhere it is anybody's guess. Storage limit of fuel containing FAME is reckoned to be 6 months only. A great deal has been written about this, so worth a search.

Having said that, in Greece I have seen no evidence of a problem. Due to ill health my tank remained full for 18 months but I experienced no problems this season.

 

[dom]

Hi Guys
Faced with the traditional winterising job of topping up the fuel tank which is a P in the A, I decided to consult the experts, in this case Hydra International Ltd who manufacture fuel additives and supplied me with my bottle of Anti-Bacterial Additive.
The engineer I spoke to did NOT recommend topping up the tank, and indeed to have as little as possible in the tank for the winter period because modern diesel fuels aren't stable for much longer than a month!
He accepts that filling the tank up reduces condensation but said that in the UK, condensation is not a big problem and what there is can be easily drained off at the primary fuel filter.
Comments?
Cheers!
Pete

He might be right!

I would broadly agree with the advice not brim the tank; rather dip it to its very bottom checking for any sediment, sludge, gum, water, etc. Also check fuel filter for any sign of water and that your tank filler-lid is 100% watertight by examining the o-ring for damage and then lubricating it. If in any doubt treat the fuel. Condensation could account for a couple of dessert spoons of water which is better than a tank of full diesel, esp as Vyv mentioned if FAME blended road diesel.

Re expected life, a lifespan of 12 moths at 25C is the normal standard. Diesel slowly oxidises over time producing gums and fine sediments. They don’t burn in the engine very well, block filters, and can consequently screw up injectors, especially new common rail ones. The expected life of diesel therefore depends on its oxidation stability and the accepted standard is that it should contain <20mg/l after being stored for 12 months at 25C. There can also be some change in composition due to the more volatile hydrocarbons evaporating first.

So, your oil friend is exaggerating? Not necessarily

As with other chemical reactions the presence of a catalyst or heat can speed-up the oxidisation process. Good installers consequently avoid copper, zinc, and their alloys. Next up, temperature, whereas 25C is the test-standard, the rate of oxidisation increases rapidly with temp. Not a problem in Old Blighty one might think but remember that the temp of the tank-return line will be a good deal higher than the tank itself. FWIW, 95C is the temp where 12 months of degradation will occur in just 25hrs and newer high-pressure common rail engines can easily heat diesel above this point! Next up, water, the anaerobic interfaces between water droplets and diesel is a nice ecosystem for anaerobic bugs and aerobic interfaces at the top of the tank is beloved by aerobic bugs. Fuel which is denatured through oxidation and in which bugs live/have-lived – esp low-sulphur diesel – is exposed to a rapid build-up of asphaltenes and their associated sludge.

On it goes. I’d advise against FAME blends if at all poss; if not then hygiene is the word: regular inspection, maintenance, treatment, and not brimming every winter.

 

[thinwater]

Next time you fill up, fill a 1-liter glass bottle at the same time and seal it. Keep it in a dark place. In my experience (and I've done this countless times with lab samples) it will keep for years.

The trouble starts when the diesel is contaminated with water (either condensation or deck leaks) and there is some corrosion (the resulting metal ions are polymerization catalysts--you can Google that). In this case, the diesel can get gummy in a few months. Same with gasoline, although things happen faster.

Thus, anti-corrosion additives are needed, in addition to a biocide. Or keep the fuel very dry.

It's not the diesel that is unstable, it is what the tank is doing to it.

 

[NormanS]

If your tank(s) is a sensible shape and properly equipped with a drainable sump, there will be no fuel/water interface. If your tank is kept full, there will be much less space for air in the tank, and therefore much less oxidation. I keep mine full.

 

[lw395]

If your tank(s) is a sensible shape and properly equipped with a drainable sump, there will be no fuel/water interface. If your tank is kept full, there will be much less space for air in the tank, and therefore much less oxidation. I keep mine full.

Regrettably, if your tank is well designed with a sump, you are in a minority of yacht owners.
Unless the tank is brimming over, the surface area exposed to the air is much the same however full it is.
When we fill up in late March, our tank is 90% fresh diesel, so if the 10% is slightly stale, it won't matter so much.

Actually we tend to be in commission 11 months of the year, but only do local trips over the winter. The diesel in the tanks gets turned over a couple of times in the late season by keeping the level fairly low.

 

[dom]

Next time you fill up, fill a 1-liter glass bottle at the same time and seal it. Keep it in a dark place. In my experience (and I've done this countless times with lab samples) it will keep for years. The trouble starts when the diesel is contaminated with water (either condensation or deck leaks) and there is some corrosion (the resulting metal ions are polymerization catalysts--you can Google that). In this case, the diesel can get gummy in a few months. Same with gasoline, although things happen faster.Thus, anti-corrosion additives are needed, in addition to a biocide. Or keep the fuel very dry.It's not the diesel that is unstable, it is what the tank is doing to it.

Sorry, if you're adopting a scientific approach then diesel's propensity to oxidation and other forms of degradation - rapid in the presence of heat and many metals - then it would be considered inherently unstable in its normal use. It is true that diesel will last a long time; I found 5l stored in an old plastic container in a hot shed and it was fine 18 years after my dad put it there! But, like your clean sealed jar, there is absolutely no scientific basis to extrapolate this to a diesel stored in a vented tank, where fuel is circulated and warmed many times through an engine, and will consequently contain at least microscopic particulate contamination, and almost certainly suffer from some water contamination at source. Most marine tanks have some water contamination. The practical approach is to recognise all of this and act accordingly.

 

[NormanS]

Sorry, if you're adopting a scientific approach then diesel's propensity to oxidation and other forms of degradation - rapid in the presence of heat and many metals - then it would be considered inherently unstable in its normal use. It is true that diesel will last a long time; I found 5l stored in an old plastic container in a hot shed and it was fine 18 years after my dad put it there! But, like your clean sealed jar, there is absolutely no scientific basis to extrapolate this to a diesel stored in a vented tank, where fuel is circulated and warmed many times through an engine, and will consequently contain at least microscopic particulate contamination, and almost certainly suffer from some water contamination at source. Most marine tanks have some water contamination. The practical approach is to recognise all of this and act accordingly.

I think that most of us on here, are talking about filling the tank for the winter, and it not being used for maybe six months. In that case heat from the return/excess fuel line, is entirely irrelevant. If the tank is pressed full, there will be little or no air present to cause oxidation. Even if not pressed full, but say an inch from the top, there will be much less volume of air. I know that you will say that the tank is vented, but if there is little or no air in the tank, what will encourage venting?
Anyway, the chances are that by the Spring, fuel will be more expensive.

 

[dom]

I think that most of us on here, are talking about filling the tank for the winter, and it not being used for maybe six months. In that case heat from the return/excess fuel line, is entirely irrelevant. If the tank is pressed full, there will be little or no air present to cause oxidation. Even if not pressed full, but say an inch from the top, there will be much less volume of air. I know that you will say that the tank is vented, but if there is little or no air in the tank, what will encourage venting?Anyway, the chances are that by the Spring, fuel will be more expensive.

All good points and you will have absolutely no problem storing perfectly dry, clean, FAME-free fuel in the manner you describe In fact, you'll almost certainly get away with road diesel during a cool British winter. Trouble, however, starts with the presence of catalysts; whether by reason of past season circulation/heat, metal contamination, microbes, asphaltenes, etc. Even if you guard against oxidation as you describe, there can still be problems with anaerobic microbes slowly multiply over winter, then speeding up in the spring. That’s why an end of season filter check and tank dipping followed by treatment and water draining if necessary is a good idea.

 

[NormanS]

We're doomed, a tell ye, we're a' doomed!
As it happens, I am lucky enough to be still using high sulfur, fame free, proper marine diesel. I have sumps with drains, and have never used snake oil, oops sorry, additives.

 

[dom]

We're doomed, a tell ye, we're a' doomed! As it happens, I am lucky enough to be still using high sulfur, fame free, proper marine diesel. I have sumps with drains, and have never used snake oil, oops sorry, additives.

Good set-up, good fuel, what's not to like - few yachts are as well configured! Class D marine diesel can legally have a sulphur content 100x that specced for trains, farm machinery etc. Don't tell the tree huggers though

 

[Graham376]

The engineer I spoke to did NOT recommend topping up the tank, and indeed to have as little as possible in the tank for the winter period because modern diesel fuels aren't stable for much longer than a month!

Absolute rubbish. Virtually all boat tanks will have a mix of fuel ages, some of which will be a year or two old as very few will allow the tank to run empty before topping up. It's 2 1/2 years since I last filled my 45 gall tank with road diesel and and dosed it with Fuel Set. The engine runs fine and no crud in the filters, same with the car which is left standing for 6 months or so each year.

 

[Leisure 27]

I have always filled my tank up in winter and never had condensation problems. Last year I heard about new diesel not lasting so I left the tank very low. On my first cruise the year after I had loads of water in the tank. I had to sail to a anchorage for the night and just managed to motor round the corner into the marina next day. A friend who filled his tank had no problems with his fuel. I am filling up this year and see what happens.

 

[Daydream believer]

If one is considering going foreign next year & has red in the tank it makes sense not to fill up until picture is clear re fuel issues. Then clean out the tank & - as seems certain- fill with fresh white.
I have had white obtained from Tescos for several years & always fill the tank at end of season.

When clearing out a section of our builders yard some years ago I found 2 concrete mixers & a diesel pump in the undergrowth that had been there for 20 years plus, that I did not know were there. One did not have a cap on the tank.
The pump started instantly. I had to bleed one mixer to get it to start & the other started after a bit of cranking. All Lister diesels & all ran Ok on the original fuel. I agree it was old fuel & not the modern stuff but it was Ok
My Seagull outboard had lain in my garage for 15 years & started easily on the petrol that was in it. Damned if it would start when I put it on the back of my dinghy, cleaned out & filled with new fuel though !!!

 

[Leisure 27]

When are we likely to know fuel laws. Are they going to fine for traces of red. How much fuel can you legally buy from a garage in a can / cans

 

[Graham376]

When are we likely to know fuel laws. Are they going to fine for traces of red. How much fuel can you legally buy from a garage in a can / cans

https://assets.publishing.service.g...e/527033/dangerous-goods-guidance-note-23.pdf

 

[benchmark]

Hi Guys
I decided to consult the experts, in this case Hydra International Ltd who manufacture fuel additives and supplied me with my bottle of Anti-Bacterial Additive.
The engineer I spoke to did NOT recommend topping up the tank, and indeed to have as little as possible in the tank for the winter period because modern diesel fuels aren't stable for much longer than a month!
He accepts that filling the tank up reduces condensation but said that in the UK, condensation is not a big problem and what there is can be easily drained off at the primary fuel filter.
Comments?
Cheers!
Pete

Well there is your problem, you are asking someone whose livelihood is based on selling additives to improve diesel.
You are better off asking a boat mechanic who routinely conserves boats for the winter and also cleans up the fuel system when there are problems.
If Diesel lasted only one month as your additive expert claims, then I would have killed my engines (both car and boat) long ago. A quick google search will prove him wrong.
At least he confessed that filling a tank up does reduce condensation, but his going further to predict exactly how the weather will be in this time of unpredictable winters and summers is foolhardy. Is he trying to say that nobody in the UK ever gets condensation problems?
Even though I have a plastic tank less subceptable to condensation, I stilltake no chances. Fill your tank up to reduce condensation and put the required dose for bug prophylaxis, don’t try to skimp on fuel or filters, the result is often very inconviniencing.