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Should a diesel tank be kept full during lay-ups?
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userPatricia
Posted: 1 January 2009 10:28 PM
Subject: Should a diesel tank be kept full during lay-ups?
 


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I have been advised that a diesel tank should be kept full during lay-ups and wonder how important this is?
usermirage
Posted: 1 January 2009 11:06 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 
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I can`t say how important it is I always keep mine topped up in winter, should prevent condensation in the tank.
userBrian Kirby
Posted: 1 January 2009 11:52 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


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Patricia - 2009-01-01 10:28 PM I have been advised that a diesel tank should be kept full during lay-ups and wonder how important this is?

Not very, but it is desirable.  As stated above, it helps to prevent condensation forming in the fuel tank, and it slows any tendency for the fuel to "wax" in very cold weather.  However, diesel fuel filters have water traps, and winter diesel stays fluid at lower temperatures, so although probably still counting as good practice, or at least wise precautions, failure to do either should not cause problems.  Running the van around for several miles every few weeks will probably compensate for lack of either precaution, and will be of greater value overall.

userRapido-lass
Posted: 2 January 2009 8:12 AM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 
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I have always been told that in winter a diesel tank should be kept full - for condensation reasons, this is for all vehicles whether laid up or not. I don't know if this is to do with old type diesel engines and whether not necessary now on the new type engines. Perhaps a petrol head can help?

I have also been told that regardless of the time of year, tanks should be kept topped up and never run low, this is so that the crap at the bottom of the tank never gets sucked up.

Thing is at some point you are going to use your vehicle and require diesel, so it's probably worth having a full tank as it's very rare the cost comes down, normally always up, so think of it as a savings tank!
usermike 202
Posted: 2 January 2009 10:10 AM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 
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I cannot understand the comment -- "tanks should be kept topped up and never run low, this is so that the crap at the bottom of the tank never gets sucked up."

The fuel pickup pipe must be at the bottom of the tank otherwise the full tank capacity could not be used and one would run out at say half a tank.

Maybee it is to do with fuel sloshing about more on an empty tank.

I never let my tank go too low in case the fuel guage is not totally accurate or there is a strike by drivers etc.
userPatricia
Posted: 2 January 2009 11:12 AM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


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Thank you all for taking the time to comment. I do normally keep the fuel high but when I returned home last time I was tired and diesel was at its most expensive. I have been meaning to top up ever since but not got round to it. However, the dreaded MOT is due in a couple of weeks so will book an earlier appointment now and fill up at the same time. My husband was always insistent that the fuel did not go too low so I never have. I think he believed that to run out of diesel would ruin the engine. However, I don't ever remember him saying anything about keeping it full over winter so I was curious to check this out.

Thank you all again for confirming that this is good practice.

Patricia
userDerek Uzzell
Posted: 2 January 2009 11:40 AM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


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It's definitely bad practice to let a diesel-fuelled vehicle run out of fuel as it can be a swine to get certain models restarted, never mind any risk of mechanical damage being caused.

Not sure if I've come across the 'keep the tank full' advice before. I can appreciate the condensation argument and I can understand that this might have been a potential problem when fuel tanks were made of mild steel and might rust internally, but most modern tanks are plastic. Anyway, it's something I've never concerned myself about.

(I do recall reading a comment about someone who, 60 or more years ago, had been told that petrol would evaporate from a fuel tank unless it was kept full and deliberately drove many extra miles to ensure that the tank was always full when the car was standing idle overnight!)
userTracker
Posted: 2 January 2009 11:49 AM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


Derek Uzzell - 2009-01-02 11:40 AM
(I do recall reading a comment about someone who, 60 or more years ago, had been told that petrol would evaporate from a fuel tank unless it was kept full and deliberately drove many extra miles to ensure that the tank was always full when the car was standing idle overnight!)


Was he Irish or was it only on April 1st Derek?
userOcsid
Posted: 2 January 2009 11:53 AM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 
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Patricia - 2009-01-01 10:28 PM

I have been advised that a diesel tank should be kept full during lay-ups and wonder how important this is?


The advice is extremely good advice.
The reason is that unlike petrol, diesel does not evaporate so the "air" void above the fuel level is basically just air, not vapour. As the weather changes so does the humidity and so does the temperature resulting in the void breathing. When the external temperature drops rapidly there is the real possibility that a humid charge in the void simply drops its laden water charge as condensation on the exposed tank walls.
Whilst this water might be caught before passing on the the engine by the sedimentor or coalescing filter it can cause real issues before then. For instance some of our motor homes have steel tanks rather than the plastic of modern cars so there is a corrosion problem complete with surface pitting and release of corrosion products. The pitting where globules of water under the fuel become particularly active due to the starvation of oxygen where the fuel is static.
However all these issues are minor relative to the presence of the water permitting biological activity breaking down the fuel on the water globule boundaries creating organic acids, surfactants, yeasts and fungal debris. The surfactants [detergents] "wetting" the coalescer element allowing the acidic water to reach the finely machined metal surfaces of the injection equipment once the engine runs again. The debris blinding the element prematurely.
However prevention is so very simple and cheap, just invest in fuel before laying up, ideally overfill into the filler neck. Make sure its from a station having a high turn over, not the tank behind the village PO.
The amount of water created is directly related to the volume of the air void and the surface area of the tank it is exposed to, so filling virtually eliminates these and the problem.
As I said the advice you were given was "extremely good", probably from my experience of this issue as good as it comes.

Edited by Ocsid 2009-01-02 11:54 AM
userBrambles
Posted: 2 January 2009 11:54 AM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


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In day gone past tanks were vented and so when fuel level fell it sucked in air This could lead to condensation. However modern vehicles use sealed tanks and as the level falls the space is filled with diesel fumes, or petrol fumes in the case of petrol tanks. This prevents condensation.

The problem is if you have summer fuel in tank and then lay up Autumn and winter - your diesel can wax up, so is desireable to dilute with winter grade fuel. Modern fuels also have a certain amount of water dispesants (diesel actually absorbes a certain amount of water anyway and contains an amount of moisture when supplied This can settle out when left stored so the fuller you tank the morewater can settle out, especially with sub zero temps. hence why filter have water traps. So basically if you keep you tank full you have more chance of water collecting.

The problem with running a tank very low is the impurities floating on top of the diesel can get sucked up. This is not so much of a problem these days with cleaner fuel stocks (mind you diesel is still pretty dirty stuff with loads of muck in it) and tanks where the pump is constamtly recycling fuel back into the tank. This tends to keep it mixed and traps any mositure and dirt that forms in the filter bowl.

Leaving tanks full during lay ups is not really a problem anymore, just leave it with what ever you have left will be fine.

Another reason for not leaving tank full is fuel degrades very quickly because of production processes used to create 'thin oil' from 'thick'. Oxidation is not so much of a problem because of sealed tank systems and additives, but the fuel can go 'stale' very quickly and hard crystaline particles form. These get trapped by the filter of course, but if you have a full tank you will get a lot more of these particles forming - hence a good reason not to have a full tank during layups.

As to moisture and condensation again, modern tanks have epoxy paint linings which resist water and fuel so prevent corrosion of the tank.

Hopefull my coments will hellp a little if you have not already fallen asleep reading.

Happy New Year and all the best in 2009 to everyone.
Jon.
userJ9withdogs
Posted: 2 January 2009 12:01 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


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As an aside - I'm glad I didn't fill the tank with fuel before laying it up for the winter. Diesel is now 30% cheaper!
userBrambles
Posted: 2 January 2009 12:21 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


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J9 - my sentiments entirely.
userTracker
Posted: 2 January 2009 12:25 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


Brambles - 2009-01-02 12:21 PM

J9 - my sentiments entirely.


Life is a merry go round of swings and roundabouts dear people and the day I start worrying about the cost of diesel is the day I'll give up Motor caravanning!

Who cares how much it costs - just do it and enjoy 'cos yer gonna be a long while dead at the end of it!
usermichele
Posted: 2 January 2009 12:32 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


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Of course fancy getting it knicked with a full tank . I would scream .
userJ9withdogs
Posted: 2 January 2009 12:45 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


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Tracker - 2009-01-02 12:25 PM

Who cares how much it costs - just do it and enjoy 'cos yer gonna be a long while dead at the end of it!


Unfortunately not everyone is in the same fortunate financial position as you, Tracker.

I still have to balance the pleasure of escaping the real world with pain of paying for it (although pleasure does usually come out on top )
userTracker
Posted: 2 January 2009 12:47 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


J9withdogs - 2009-01-02 12:45 PM

Tracker - 2009-01-02 12:25 PM

Who cares how much it costs - just do it and enjoy 'cos yer gonna be a long while dead at the end of it!


Unfortunately not everyone is in the same fortunate financial position as you, Tracker.

I still have to balance the pleasure of escaping the real world with pain of paying for it (although pleasure does usually come out on top )


Fair comment Janine - and all I can add is - lucky old pleasure - usually!
userBrambles
Posted: 2 January 2009 12:53 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


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Derek Uzzell - 2009-01-02 11:40 AM

(I do recall reading a comment about someone who, 60 or more years ago, had been told that petrol would evaporate from a fuel tank unless it was kept full and deliberately drove many extra miles to ensure that the tank was always full when the car was standing idle overnight!)


Hi Derek, Makes me think of people today who will drive out of their way to save a penny a litre using up the saving to get there!
userClive
Posted: 2 January 2009 11:08 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


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The original reason for keeping the diesel tank full was to limit the amount of tank that could suffer from oxidization (rust) due to condensation on the inside of the tank. However today most tanks are plastic so this problem should not happen. But any condensation can cause a gradual build up of water in your fuel tank if left for a very long time. Also if anyone steals your pride and joy a full tank of fuel will be to their advantage.
C.



userDerek Uzzell
Posted: 3 January 2009 9:46 AM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


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Interesting that there have been two comprehensive, but (seemingly) opposite, replies to Patricia's question.

One things for sure - when the 'chassis' on which a motorcaravan will be built rolls out of the factory its fuel tank won't be full and, when it hangs around somewhere waiting for the conversion to be carried out, the tank still won't be full. And when it languishes (for Heaven knows how long nowadays) on a dealer's forecourt, it's still very unlikely to have a full fuel tank. As this doesn't appear to have any adverse effect on the longevity of new motorhomes' motors (or at least I've never heard it mentioned), I'm doubtful that leaving a tank part-full during winter lay-ups will cause real-world harm. I'll bet that some larger motorhome dealers have secondhand vehicles with fuel-tanks that have been near empty for months and months and months.
userGeorge Collings
Posted: 3 January 2009 10:40 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 
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Tanks are not totally sealed, if this was the case, as fuel was pumped out the tank would collapse due to atmospheric pressure.

Fortunatly I have not had to play with tank venting for many a year so am not aware of the exact arrangemnts now used. Can anybody enlighten us.

In the mean time I shall keep my tank full and keep checking the water trap on the filter two or three times a year just in case I pick up some water when refueling.

The fuel pick up on my VW T4 was only about 2 mm from the flat bottom of the plastic tank where it would have hoovered up water or debris before any significant accumulation occurred and delivered it to the filter.

The tank came out during a long gremlin hunt where fuel chokage was suspected. Was it hell. The fault was a poor electrical connection on the pump stop solenoid.

Sods Law rules OK.

userBrambles
Posted: 4 January 2009 10:05 AM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


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"Fortunatly I have not had to play with tank venting for many a year so am not aware of the exact arrangemnts now used. Can anybody enlighten us. "

Diesel tanks systems are now sealed.
Petrol is semi sealed, there is a valve and vapour trap which feeds vapours into air induction sytem of the engine.
Tanks can collapse under certain conditions but is very rare.
Bear in mind you do not get a total vacuum, there is only partial drop in pressure or in the case of petrol, increase in pressure. As fuel is drawn off the drop in pressure aids vapourisation of the fuel to equalise the pressure.

userRupertGS
Posted: 4 January 2009 12:29 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 
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I have a very complicated scheme for management of my diesel tank. Any reader interested may wish to get a pencil and paper now and make notes.

I fill up my tank to the brim and I then drive it until a little yellow warning light on my fuel guage comes on. I know that this gives me a further 80 or so miles of driving, so the secret is not to panic!

I then pull in to the next filling station and I fill it to the brim again. The secret is to repeat this process continually and eventually it becomes second nature.

It certainly works for me and I've never had a problem when I lay up my 'van for a few weeks with the tank full, half empty or almost empty.

usermikeyb
Posted: 6 January 2009 1:02 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 
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RupertGS, what a brilliant idea! the whole answer in a nutshell. However, I do have to take issue with you on one point. What grade of pencil should I use? Too soft, and it might wear out too quickly. Too hard, and the point could be dangerous....Health and Safety remember.
Mike.
userMelvynT
Posted: 6 January 2009 1:25 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 
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After reading all the responses, it boils down to use your motorhome and it will not be a problem.
Diesel tanks don't rust any faster than the metal body, this will be the first thing to rust through.
Petrol tanks might, I've had a 1960's car go like this but the body was shot by this time anyway.
usertonyishuk
Posted: 13 October 2016 2:32 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 


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Having started this year with the "water in the fuel" light on, I thought I would take a look at views on whether to top up, or leave empty.

I found the following link, which might be of interest.

http://forums.sailinganarchy.com/index.php?showtopic=153377

Pockets must be deeper than mine, if I had to fill 2 X 650 litre tanks with diesel.

Still none the wiser.

Rgds
userhagrid
Posted: 13 October 2016 8:15 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 
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I haven't read all the posts but will comment based on accumulated knowledge.

Keeping the tank topped up reduces the risk of condensation ( water) in the tank.
Modern diesel contains a % of bio diesel, more so in summer than winter.
Bio Diesel and water can encourage the growth of algae commonly known as diesel bug.
If diesel bug becomes established, it blocks fuel filters and is very difficult to eradicate.

My advise would be to ensure that your tank is filled after October, dose it with soltron or a similar anti bug treatment and keep it topped up during periods of lay up.

userDucto
Posted: 13 October 2016 10:00 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 
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Short one is yes; I would say.

Put some diesel bug in for long lay-ups. Yachties do this over wintering in the boatyard.
userQFour
Posted: 13 October 2016 10:48 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 
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If you are laying it up then you should be worrying more about the brakes and tyres than the diesel. Commercial vehicles are not designed to be laid up for the winter. Put some warm clothes in and get out and use it.
userColin Leake
Posted: 14 October 2016 7:43 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 
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One of my neighbours who has a canal boat tells me that bugs in the tanks of canal boats causing a sludge in the tanks bottom is such a common problem that mobile specialist firms exist to pump out the tanks, clean the bottom out and refill with fresh treated diesel. He always uses a additive in his before the winter layup.

I use a petrol extender in my garden machines and generator over the winter.

Like others on here I take our motorhome out for a 40 or 50 mile round trip once a month. Gives us a nice day out somewhere.

Edited by Colin Leake 2016-10-14 7:46 PM
useraandncaravan
Posted: 14 October 2016 9:51 PM
Subject: RE: Should a diesel tank be kept full during lay-ups?
 
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There are multiple considerations:

Modern Diesel fuel both deteriorates faster and promotes the formation of Diesel bug than did the fuel formulations of a couple of years ago.
The high Sulphur level, reduced in 2012 and again in 2015?, was allegedly very good at both keeping Diesel bug at bay and preventing Diesel from degrading.
Modern low Sulphur Diesel should be regarded as having a max 4 - 6 month life, maybe less?, without treatment.

So things have changed a lot in the last couple of years. We would suggest that, unless you have an old Van with a Steel fuel tank, that you keep the fuel level as low as practical when the van is not in use.

This ensures that when you do use it, a full tank of fresh fuel means that the degraded fuel is 'swamped' by the fresh reducing the risk of issues.


If you have an old vehicle with Steel Tank (probably 20 + years old?) then keep it topped up as high as possible to prevent the Tank rusting. You only need the tiniest particle of rust to lead to Injector problems.
However, this may give issues with degradation and Diesel Bug so an anti-Bug additive would be a very good idea.

I have noticed that the Petrol in my 'Classic' 1973 Motorbike, which hardly gets used, has almost no octane value by 4 months and is a jelly by 12 months.
Yet I can remember the days not that long ago (alright 20 years) when an old bike/car could pulled out of a very long slumber and fired up without any issues.

Many of the old Citroen vans that we used to specialise in that came to us after being static for a while needed a Petrol Tank Flush. The Diesel vans often had a Tar like substance lining the tank that looked like someone had been trying to run it on Bitumen.
I took a lot of convincing it was the by-product of Diesel Bug. It was such a hard Tar like substance I found it hard to believe it could be produced by an Algae or whatever the 'Bug' is.





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