Keeping The Fuel Tank Full

[Doorman]

.... and that BIO-diesel is MUCH MORE hygroscopic - maybe it will come to pass that silica-gel traps in breathers will be more common in months to come as we are forced to use more Bio-diesel... I wonder why it gets to settle in a layer separate from the diesel and doesn't get absorbed by the diesel

 

Nick

 

The answer maybe in the name 'water separator' :-}

 

Mike

 

A few monthsd ago I went into Sainsburys at Nantwich and there was a van on the forecourt that was apparently cleaning the fuel by pumping it out of the tanks and passing through the kit in the van and back into the tanks. I'm pretty certain it was the diesel they were doing, but whether it was a routine thing or in response to a particular event I can't say.

 

 

A marine engineer we knew back up norf, was investigating the viability of setting up a new business, conducting a diesel cleansing service such as you described. He claimed that such a service was becoming vital, with the introduction of the higher percentage Bio-fuel content.

 

Mike

[Guest]

I fill mine close to the top, and bung some Marine 16 in it. Jobs a goodun. Never fill completely, leave a small air gap.

[NB Alnwick]

Despite all that has been said about fuel 'going off' over time, when we sold our MGB in April, it started and drove off perfectly well and we hadn't put any 'new' petrol in it since 2007. At least half of the fuel must have been much older as we had only refilled it on that one occasion since 2005.

 

I guess it all depends on the circumstances, such as the cleanliness of the tank, together with the temperature and moisture content of the storage environment.

[DandV]

From my experience as an oil company engineer responsible for fuel dispensing installations and therefore involved with resolving customer complaints regarding fuel quality, recreational boat fuel provided a disproportionate number of problems.

 

In almost all cases the problems could be ascribed to the configuration of the fuel tanks on board and the operating regime. Flush deck mounted filling points are prone to water ingress compared to road vehicle fill points. It is important that they are kept correctly tightened and the seals regularly inspected and replaced when necessary. In some boats the location of the breather openings also facilitated water ingress especially in heavy seas and torrential rain. Boat tanks are often subject to large temperature variations on a daily basis which means a large transfer of air and vapour outwards during the daytime heating phase and a replacement with outside air including its attendant water vapour and bug inducing yeasts during the night cooling period. The water vapour condenses and accumulates in the tank. As the air/vapour expands and contracts a lot more then the liquid fuel then it follows that keeping tanks full reduces condensation problems. Another problem is upon cooling the water condenses on the unwetted inner surfaces of the tank initiating surface rusting. This rust can then be later dislodged and migrate through the fuel system to block filters and in extreme cases I have seen actually perforate the fuel tank. On pleasure boats the problem is exacerbated because fuel tanks are often large to give range but because of the cost and weight, operators tend to run them on near empty.

 

A graphic illustration of internal condensation in fuel tanks on underground fuel tanks is the rust stain that develops on the tank floor directly below and exactly mirroring the manway above. The tanks are completely surrounded by sand that provides insulation except for a manway which is generally uncovered in a pit through which the tank top fittings penetrate. This provides the cold surface for the water to condense before dropping through the fuel to stain the tank bottom.

 

On using biocides my view is strongly that they are not a substitute for fuel housekeeping. First efforts should always be made to prevent water ingress and then to have the hardware (filters) and operating regime to remove the inevitable water/crud that does get past. On aviation tanks the regime is a daily tank bottom and filter bowl water check but it would still be a negligent operator who did not check his aircraft fuel for water daily as well.

Biocides are extremely toxic , and dead bug blocks filters just as much as live bug. In twenty years I never raised an order for dosing fuel tanks and I know of one contractor seriously poisoned doing so.

 

Edit to change egress to ingress

Edited September 10, 2010 by DandV

[Liam]

For all those of you who reply to say that you keep yours filled, I hope you also keep it locked!

[Doorman]

From my experience as an oil company engineer responsible for fuel dispensing installations and therefore involved with resolving customer complaints regarding fuel quality, boat fuel provided a disproportionate number of problems.

 

In almost all cases the problems could be ascribed to the configuration of the fuel tanks on board and the operating regime. Flush deck mounted filling points are prone to water ingress compared to road vehicle fill points. It is important that they are kept correctly tightened and the seals regularly inspected and replaced when necessary. In some boats the location of the breather openings also facilitated water ingress especially in heavy seas and torrential rain. Boat tanks are often subject to large temperature variations on a daily basis which means a large transfer of air and vapour outwards during the daytime heating phase and a replacement with outside air including its attendant water vapour and bug inducing yeasts during the night cooling period. The water vapour condenses and accumulates in the tank. As the air/vapour expands and contracts a lot more then the liquid fuel then it follows that keeping tanks full reduces condensation problems. Another problem is upon cooling the water condenses on the unwetted inner surfaces of the tank initiating surface rusting. This rust can then be later dislodged and migrate through the fuel system to block filters and in extreme cases I have seen actually perforate the fuel tank. On pleasure boats the problem is exacerbated because fuel tanks are often large to give range but because of the cost and weight, operators tend to run them on near empty.

 

A graphic illustration of internal condensation in fuel tanks on underground fuel tanks is the rust stain that develops on the tank floor directly below and exactly mirroring the manway above. The tanks are completely surrounded by sand that provides insulation except for a manway which is generally uncovered in a pit through which the tank top fittings penetrate. This provides the cold surface for the water to condense before dropping through the fuel to stain the tank bottom.

 

On using biocides my view is strongly that they are not a substitute for fuel housekeeping. First efforts should always be made to prevent water egress and then to have the hardware (filters) and operating regime to remove the inevitable water/crud that does get past. On aviation tanks the regime is a daily tank bottom and filter bowl water check but it would still be a negligent operator who did not check his aircraft fuel for water daily as well.

Biocides are extremely toxic , and dead bug blocks filters just as much as live bug. In twenty years I never raised an order for dosing fuel tanks and I know of one contractor seriously poisoned doing so.

 

Excellent information. Cheers!

 

For all those of you who reply to say that you keep yours filled, I hope you also keep it locked!

 

 

 

Only when passing through Partington! ;-)

[BGA]

I dont own a boat so I dont know the answer to this, are boats normally fitted with a water trap in the fuel line, I know light aircraft are and they are checked before each flight. I know this wouldn't remove water collected in the tank but surely a small electric pump (windscreen washer pump would probably do it) with a pipe to the lowest part of the tank would remove all the water quite quickly, run it into a glass jar, all the water will sink to the bottom.

[Nickhlx]

Excellent information. Cheers!

 

 

 

 

 

Only when passing through Partington! ;-)

 

 

What's the significance of Partington ?

 

Nick

[Guest]

What's the significance of Partington ?

 

Nick

 

My guess would be somebody had their fuel syphoned off there (wherever it is mind..)

[WJM]

"are boats normally fitted with a water trap in the fuel line"

 

There is usually a water trap in the fuel line just before the engine. The shape of narrowboat tanks usually make an aircraft type water drain impossible. Tanks tend to be totally flat bottomed because they are formed by damming off the tail of the boat ie: the baseplate of the boat is the base of the tank. Sucking a layer of water 1 millimetre thick, one metre square would be impossible.

[NB Alnwick]

From my experience as an oil company engineer responsible for fuel dispensing installations and therefore involved with resolving customer complaints regarding fuel quality, recreational boat fuel provided a disproportionate number of problems.

 

In almost all cases the problems could be ascribed to the configuration of the fuel tanks on board and the operating regime. Flush deck mounted filling points are prone to water ingress compared to road vehicle fill points. It is important that they are kept correctly tightened and the seals regularly inspected and replaced when necessary. In some boats the location of the breather openings also facilitated water ingress especially in heavy seas and torrential rain. Boat tanks are often subject to large temperature variations on a daily basis which means a large transfer of air and vapour outwards during the daytime heating phase and a replacement with outside air including its attendant water vapour and bug inducing yeasts during the night cooling period. The water vapour condenses and accumulates in the tank. As the air/vapour expands and contracts a lot more then the liquid fuel then it follows that keeping tanks full reduces condensation problems. Another problem is upon cooling the water condenses on the unwetted inner surfaces of the tank initiating surface rusting. This rust can then be later dislodged and migrate through the fuel system to block filters and in extreme cases I have seen actually perforate the fuel tank. On pleasure boats the problem is exacerbated because fuel tanks are often large to give range but because of the cost and weight, operators tend to run them on near empty.

 

A graphic illustration of internal condensation in fuel tanks on underground fuel tanks is the rust stain that develops on the tank floor directly below and exactly mirroring the manway above. The tanks are completely surrounded by sand that provides insulation except for a manway which is generally uncovered in a pit through which the tank top fittings penetrate. This provides the cold surface for the water to condense before dropping through the fuel to stain the tank bottom.

 

On using biocides my view is strongly that they are not a substitute for fuel housekeeping. First efforts should always be made to prevent water ingress and then to have the hardware (filters) and operating regime to remove the inevitable water/crud that does get past. On aviation tanks the regime is a daily tank bottom and filter bowl water check but it would still be a negligent operator who did not check his aircraft fuel for water daily as well.

Biocides are extremely toxic , and dead bug blocks filters just as much as live bug. In twenty years I never raised an order for dosing fuel tanks and I know of one contractor seriously poisoned doing so.

 

Edit to change egress to ingress

 

I think this is an excellent answer to Alan's question. If like with our tank, the diesel tank is integral with the boat's baseplate it is probably best to keep the tank topped up whenever practical. At least we are fortunate in that our tank filler and vent are located high up on the cabin roof, safely away from the usual contaminants.

[waterman]

Just to add to the discussion, I think there are some guestimates on how much old fuel is left each year. By old fuel I mean of the original full tank

 

To be precise the amounts are as follows.

 

 

 

Year % of original fuel

 

1 80%

 

2 64

 

3 51.2

 

4 40.96

 

5 32.77

 

6 26.21

 

7 20.97

 

8 16.78

 

9 13.42

 

10 10.74

 

 

 

Some of you will say that if 10.74% is original fuel then 69.26 must be between 1 and 9 years old. The other 20% is the new 40 lt of fuel.

 

 

 

Is this an end to the discussion, I think not, unless you know different?

 

 

[mayalld]

Just to add to the discussion, I think there are some guestimates on how much old fuel is left each year. By old fuel I mean of the original full tank

 

To be precise the amounts are as follows.

 

 

 

Year % of original fuel

 

1 80%

 

2 64

 

3 51.2

 

4 40.96

 

5 32.77

 

6 26.21

 

7 20.97

 

8 16.78

 

9 13.42

 

10 10.74

 

 

 

Some of you will say that if 10.74% is original fuel then 69.26 must be between 1 and 9 years old. The other 20% is the new 40 lt of fuel.

 

 

 

Is this an end to the discussion, I think not, unless you know different?

 

 

 

well, given that I already gave the same figures (in litres, rather than percentages) quite a few posts back, no it won't put an end to the discussion.

[waterman]

Just to add to the discussion, I think there are some guestimates on how much old fuel is left each year. By old fuel I mean of the original full tank

 

To be precise the amounts are as follows.

 

 

 

Year % of original fuel

 

1 80%

 

2 64

 

3 51.2

 

4 40.96

 

5 32.77

 

6 26.21

 

7 20.97

 

8 16.78

 

9 13.42

 

10 10.74

 

 

 

Some of you will say that if 10.74% is original fuel then 69.26 must be between 1 and 9 years old. The other 20% is the new 40 lt of fuel.

 

 

 

Is this an end to the discussion, I think not, unless you know different?

 

 

[Nickhlx]

well, given that I already gave the same figures (in litres, rather than percentages) quite a few posts back, no it won't put an end to the discussion.

 

 

Does it assume that the fuel is always kept perfectly mixed ? Is this a fair assumption ? Does it matter ?

 

Nick

[mayalld]

Does it assume that the fuel is always kept perfectly mixed ? Is this a fair assumption ? Does it matter ?

 

Nick

 

I think that it is probably a sufficiently reasonable assumption, particularly given that refueling always happens after the annual cruise.

[Nickhlx]

Groundhog Day ?

 

Nick

 

 

[waterman]

Sorry nick, I did not see your reply in Lt, I did not mean to Plagiarise your , I just read the first few replies and put the numbers into a spread sheet

As you say this will rumble on and on, personally I keep my NB tank full over the winter and run it down during the summer season.

[Nickhlx]

Sorry nick, I did not see your reply in Lt, I did not mean to Plagiarise your , I just read the first few replies and put the numbers into a spread sheet

As you say this will rumble on and on, personally I keep my NB tank full over the winter and run it down during the summer season.

 

 

No worries - I thought the system was duplicating messages or something...

 

We are currently a light / low user, and I am currently drawing up plans to have a small "day" tank specially made to fit available space, with a capacity of about 60 litres. This will be used most of the time, be very easy to drain / flush ( tapered / conical bottom) and the main tank will be emptied - possibly filled / used if we start doing longer trips - the boat was intended to be a CC and in use for long periods of the year ( and may still be one day) but at the moment my wife's illness is not permitting that to happen. With the coming of the new fuel with more Bio-diesel content, current fuel related problems will only likely get worse. Also the holding of smaller amounts of fuel will minimise loss in the event of someone thieving it.

 

Nick

[nb Innisfree]

Every year I tilt our nb to starboard and stick a rigid length of 15mm plastic plumbing pipe with a w/m hose tap inline through the filler and into the lower starboard corner of diesel tank, this connects to a Pela oil extractor. Close valve, pump the extractor until a good vacuum is obtained and open valve, water in the bottom of tank is withdrawn. Job done

[Guest]

Every year I tilt our nb to starboard and stick a rigid length of 15mm plastic plumbing pipe with a w/m hose tap inline through the filler and into the lower starboard corner of diesel tank, this connects to a Pela oil extractor. Close valve, pump the extractor until a good vacuum is obtained and open valve, water in the bottom of tank is withdrawn. Job done

Aye,me an'all. Usually get a around litre of water out,and sometimes stuff that looks like pink porridge.

[onthecut]

From personal experience, I think aiming to keep the tank full definitely works in terms of minimising moisture contamination. Our tank is a typical stern / counter type and at least once in a year I put a syphon pump with clear pick up pipe down to the bottom and draw up a sample. I have yet to see any discernible sign of water. As mentioned elsewhere, it also serves to minimise the surface area liable to corrosion. Strikes me that ageing of Diesel fuel is prewtty much a non-issue. We regularly get engines in at work that may have stood ten years or more, but none the less have some residual fuel in the tank or pipes. A little fettling and those not otherwise incapacitated seem to come to life quite happily on this ancient fuel.

For those who prefer to run the tank low and then don't use the fuel out of the cruising season, why not simply plug the vent ?

 

Mike.

[RLWP]

From personal experience, I think aiming to keep the tank full definitely works in terms of minimising moisture contamination. Our tank is a typical stern / counter type and at least once in a year I put a syphon pump with clear pick up pipe down to the bottom and draw up a sample. I have yet to see any discernible sign of water. As mentioned elsewhere, it also serves to minimise the surface area liable to corrosion. Strikes me that ageing of Diesel fuel is prewtty much a non-issue. We regularly get engines in at work that may have stood ten years or more, but none the less have some residual fuel in the tank or pipes. A little fettling and those not otherwise incapacitated seem to come to life quite happily on this ancient fuel.

For those who prefer to run the tank low and then don't use the fuel out of the cruising season, why not simply plug the vent ?

 

Mike.

 

I don't think a BSS compliant tank vent can be plugged.

 

<Richard imagines all the problems with collapsed fuel tanks and stopped engines in the spring as boaters forget to unplug their tank vents>

 

Richard

[Nickhlx]

I don't think a BSS compliant tank vent can be plugged.

 

<Richard imagines all the problems with collapsed fuel tanks and stopped engines in the spring as boaters forget to unplug their tank vents>

 

Richard

 

 

 

OK - to take the point further then, why not have a "ignition" operated solenoid valve which opens the vent line when the engine is running, or fit that silical-gel canister in the vent line ?

 

Nick

[RLWP]

OK - to take the point further then, why not have a "ignition" operated solenoid valve which opens the vent line when the engine is running, or fit that silical-gel canister in the vent line ?

 

Nick

 

I don't like your first suggestion, as if it failed, you still get the same problems I described above

 

Do like the second one though, although it may spend a lot of it's time trying to dehumidify the great outdoors

 

Richard