DIY fuel polishing in practice.

[pcatterall]

Being the proud owner/builder of a brand new fuel polishing system I thought I would give it a go and report back!!
I did have 5 gallons of the red stuff which I had rescued after cleaning my tanks, this was the stuff from the bottom and very black.
This has settled over the last 6 months, there was a darker layer on the lower 3" of the container.
I did my first filter using the hose only part way into the tank thus avoiding the nastiest of the black stuff. I compared the 'filtered' fuel with that in the top half of the original container. There was no discernable difference in colour.... not quite gleaming ruby red, slightly brown but not bad ( I may try some photos!).
I continued filtering with the pipe held just above the mucky stuff in the bottom.
I then poured the bottom layer into a glass container ( it was opaque when held to the light) I then filtered this into another glass container, it seemed only marginally clearer, I filtered it 5 times in this manner and it seemed to get clearer every time untill it became as clear as the first sample.
So assuming that colour is at least a guide to cleanliness ( and it may not be the whole story) really dirty fuel took five passes to clear it. This concerned me a little because in a 'boat situation' the filter only gets one pass.
Does this imply that if we leave our boat in a nice calm situation for a week or more then start up and drive away then the potentially dirty fuel ( which is the first to be drawn up) will not be filtered as well as it should be?
The filter element I used was 5 to 7 microns and my ( before this test) understanding was that ( in theory) any particle over that size would be caught in the filter which would do that job until the filter blocked or was changed. I recognised that this was 'in theory' but didn't consider that 5 passes would show continual improvement.
These results suggest (to me) that a polishing regime should be as follows.
Ideally after the boat has been 'steady' for a day or so 'Polish' the lower 5 gallons into a seperate container, if the fuel looks mucky then dont return it to the tank but circulate just the fuel in the container through the filter until it is clean.
I recognise that there are practical issues here with pipework ( connections on and off or valves) but the alternative would be to polish the contents of the whole tank 5 times in order to be sure that the small really dirty portion was clean.
This trial has certainly made me think again on fuel issues.
It WAS a cheap CAV type filter so possibly a more efficient one would have cleaned the fuel on the first pass??
Would there be an advantage in just using the polishing system ( at least for the bottom few gallons) prior to starting whenever the boat has been standing a while? Just one pass would at least mean that all the bottom gunk would be distributed over the whole tank rather than it all being drawn through the filter when you start up.

 

[theoldsalt]

Many engines "polish" the diesel as part of the normal function of the fuel system. The lift pump supplies far more fuel to the injector pump than is needed for the engine to run. This excess is passed back to tank. So the fuel is continually being filtered many times.

The fuel take-up in the tank does not normally reach the very bottom of the tank but the rolling and piching of a boat at sea can be enough to keep the fuel mixing in the tank

 

[Boreades]

There's a very well-detailed (but understandable) thread here on SailBoatOwner

Executive summary: Use cheap filters and change them regularly.

In my case, that means buying the Bosch car/van filter that is a pattern match for the Volvo version.

 

[NormanS]

All this can so easily be avoided if the tank has a sump with an accessible drain valve. Any motion of the fuel in the tank encourages any water or "mucky stuff" to fall into the sump. Experience of your own system will tell you how often to test with the drain valve.

 

[Heckler]

Being the proud owner/builder of a brand new fuel polishing system I thought I would give it a go and report back!!
I did have 5 gallons of the red stuff which I had rescued after cleaning my tanks, this was the stuff from the bottom and very black.
This has settled over the last 6 months, there was a darker layer on the lower 3" of the container.
I did my first filter using the hose only part way into the tank thus avoiding the nastiest of the black stuff. I compared the 'filtered' fuel with that in the top half of the original container. There was no discernable difference in colour.... not quite gleaming ruby red, slightly brown but not bad ( I may try some photos!).
I continued filtering with the pipe held just above the mucky stuff in the bottom.
I then poured the bottom layer into a glass container ( it was opaque when held to the light) I then filtered this into another glass container, it seemed only marginally clearer, I filtered it 5 times in this manner and it seemed to get clearer every time untill it became as clear as the first sample.
So assuming that colour is at least a guide to cleanliness ( and it may not be the whole story) really dirty fuel took five passes to clear it. This concerned me a little because in a 'boat situation' the filter only gets one pass.
Does this imply that if we leave our boat in a nice calm situation for a week or more then start up and drive away then the potentially dirty fuel ( which is the first to be drawn up) will not be filtered as well as it should be?
The filter element I used was 5 to 7 microns and my ( before this test) understanding was that ( in theory) any particle over that size would be caught in the filter which would do that job until the filter blocked or was changed. I recognised that this was 'in theory' but didn't consider that 5 passes would show continual improvement.
These results suggest (to me) that a polishing regime should be as follows.
Ideally after the boat has been 'steady' for a day or so 'Polish' the lower 5 gallons into a seperate container, if the fuel looks mucky then dont return it to the tank but circulate just the fuel in the container through the filter until it is clean.
I recognise that there are practical issues here with pipework ( connections on and off or valves) but the alternative would be to polish the contents of the whole tank 5 times in order to be sure that the small really dirty portion was clean.
This trial has certainly made me think again on fuel issues.
It WAS a cheap CAV type filter so possibly a more efficient one would have cleaned the fuel on the first pass??
Would there be an advantage in just using the polishing system ( at least for the bottom few gallons) prior to starting whenever the boat has been standing a while? Just one pass would at least mean that all the bottom gunk would be distributed over the whole tank rather than it all being drawn through the filter when you start up.

Peter
as the filter gets blocked, it polishes more, thats why the repeated passes make it more efficient
Stu

 

[TradewindSailor]

Make sure the tank is clean

Slightly off topic perhaps:

Running the fuel through filters is okay for cleaning the fuel but not the tank.

Black slime will attach itself to the walls of the tank and to the sides of the baffles. In rough seas this slime can break loose and may get sucked up the intake, possibly blocking it. It would certainly start blocking the filters.

There are a number of good defences:

If the tank has an inspection hatch and has no internal baffles, the tank itself can be cleaned .... and seen to be clean.

A day running tank can be installed that is filled with filtered fuel from the main tank. If plumbed independently it also gives an alternative supply of fuel if the other gets blocked.

Duplicate the filter system so that one set of filters can be switched in if the other gets blocked.

Install a vacuum gauge to check the condition of the filters.

Install an in-line diaphram fuel pump that can be turned on to aid filling the day tank, polish the fuel, and prime the engine.

Make sure the jerry cans are clean and the seals on the deck filling caps are in good condition. Also check that the tank vents are clear and protected.


I never use biocide or alcohol to absorb the water into the fuel. I just keep the tank clean and keep a good eye on the filters.

 

[Boreades]

Re "If the tank has an inspection hatch and has no internal baffles, the tank itself can be cleaned .... and seen to be clean."

What's best for this kind of cleaning?

 

[GrahamM376]

All this can so easily be avoided if the tank has a sump with an accessible drain valve. Any motion of the fuel in the tank encourages any water or "mucky stuff" to fall into the sump. Experience of your own system will tell you how often to test with the drain valve.

In an ideal world, boat tanks would be like aircraft ones with a sump and drain cock in the bottom. Would be very easy to take a sample regularly and drain any water or crud.

 

[pcatterall]

"What's best for this kind of cleaning?"
I just reduced the fuel by pumping into containers then got stuck in with a brush and torch.
In my tanks there was just a coating of black slime on the walls, ( heavier further down and on the bottom) I just scrubbed and stired it all up then pumped the tank dry. The really filthy bottom gallon I just disposed of. There was also about 5 gallons of very dirty fuel which I saved. This is the fuel that I tested my polishing system with. It had settled out over the weeks in the garage to the extent that the top 4 gallons showed no improvement after filtering but ( as stated ) the bottom gallon took 5 passes to clear.

 

[pcatterall]

"Peter
as the filter gets blocked, it polishes more, thats why the repeated passes make it more efficient
Stu"

Interesting comment from Skipper Stu

I can see that fuel passing through a partially blocked filter will have to work harder to get through and may deposit more as it passes through.

Does this mean, then, that a mucky filter is more efficient!

 

[Roberto]

Re "If the tank has an inspection hatch and has no internal baffles, the tank itself can be cleaned .... and seen to be clean."

What's best for this kind of cleaning?

I have a tank with a large inspection hatch, on average the tank is very clean, I open the hatch twice a year and suck up the (very limited) powdery residue sticking to the tank walls with a Pela pump

It is a vacuum pump used for oil change, it has a tiny flexible metal pipe (like bowden) which is perfect to go hunting the black residue without stirring up the whole content

 

[boatmike]

"Peter
as the filter gets blocked, it polishes more, thats why the repeated passes make it more efficient
Stu"

Interesting comment from Skipper Stu

I can see that fuel passing through a partially blocked filter will have to work harder to get through and may deposit more as it passes through.

Does this mean, then, that a mucky filter is more efficient!

In some respects yes. The ratings of filters is often misunderstood. There is "absolute" and "nominal" Absolute rated filters are used generally as "last chance" filters such on the fuel pump inlet. They generally are not expected to have a high dirt holding capacity as most of the cleaning is expected to take place beforehand. The "nominal" filter at say a 5 micron rating will not stop all 5 micron particles as new. The rating is meant to indicate the "nominal" size of particles it will stop over its useful life. When new the differential pressure on such a filter will be very low but will rise somewhat over its life as it holds more and more dirt. When it reaches its rated dirt holding capacity the DP will rise to a maximum above which there is a danger of high DP causing the filter to "shed" some of this contamination. Many (not all) filter holders have a pressure bypass valve set at this level to stop the filter shedding. It is better to by pass the filter with mildly contaminated oil or fuel than to have the filter break down and dump its load. Therefore you are technically right that a contaminated filter will be marginally more efficient in stopping smaller particles up to its maximum DP and dirt holding. Above that beware!

BTW don't judge the contamination of fuel or oil by it's colour. This can be affected by many things and is actually a pretty poor indication of the amount of dirt in the fuel.
One of the biggest enemies in the diesel world is biological growth which technically isn't a matter of particle size. The sludge is a biomass which can block pipes and filters quite quickly but can by the introduction of ensymes be broken down into a substance which does not congeal into big gooey lumps and can pass through filters..... I pass no judgement on these additives but would personally rely on circulating the diesel through an efficient cyclone filter and water seperator of about 15/25 micron rather than trying to filter it out with a finer filter in the fuel line. In any boat I have owned I have fitted an inline 20 micron filter of this type followed by a conventional filter of 15 micron and a final filter of 5/7 microns (usually fitted on the engine anyway). As someone else said there is a natural circulation of diesel through the tank return line anyway so such a setup should keep your system healthy without adding anything to the fuel. Prevention is better than cure!

 

[lw395]

I have a tank with a large inspection hatch, on average the tank is very clean, I open the hatch twice a year and suck up the (very limited) powdery residue sticking to the tank walls with a Pela pump

It is a vacuum pump used for oil change, it has a tiny flexible metal pipe (like bowden) which is perfect to go hunting the black residue without stirring up the whole content

+1.

I used to take the dirty fuel I'd extracted home and leave it to settle in 2 pint polythene milk bottles. After a while you can pour off the clean stuff from the top, and return it to the tank.
The gunk goes to the council waste oil tank.

 

[KevinT1]

+1.

I used to take the dirty fuel I'd extracted home and leave it to settle in 2 pint polythene milk bottles. After a while you can pour off the clean stuff from the top, and return it to the tank.
The gunk goes to the council waste oil tank.

Likewise - after my dear son topped up the diesel tank with fresh water I pumped out 5 gallons of the stuff before it came clean.

I'm pretty sure the previous owner had also filled the diesel tanks with water at some point

I then took the top off the tank and used my Pela to "vacuum" the tank"

Let it all settle and managed to recover most - only last few litres have been ditched.

Something very satisfying about vaccuming the inside of your diesel tank

 

[NormanS]

In an ideal world, boat tanks would be like aircraft ones with a sump and drain cock in the bottom. Would be very easy to take a sample regularly and drain any water or crud.

Lucky me. I live in an ideal world. I think I can say that all boat tanks used to be made this way. The prevelance of "modern" flat bottomed yachts, has made it more difficult to install perfect tanks.

 

[gandy]

If you can once get the tank clean, I personally would prefer to draw from the very bottom, and not allow space for crud and water to accumulate. On a sailing boat it doesn't seem a good idea to let all the crud build up ready for the day when the weather's just rough enough to stir it up, and your engine suddenly gets several years' worth of crud all at once.

 

[Marsupial]

"This concerned me a little because in a 'boat situation' the filter only gets one pass."

not so, the fuel goes through the fuel system, some of it is injected to make the engine work the rest is returned to the tank to be picked up filtered again and again, engines polish the fuel constantly in normal operation. Fitting extra and larger filters will delay blockages with contaminated fuel, OR use enzyme fuel treatments to break down the contaminants so they pass through filters - no need to polish anything.

 

[noelex]

The amount of "polishing" that occurs via the diesel return is very small.
A rough calculation shows my inbuilt polishing system filter about 500x more fuel than than that filtered by the diesel return.

By collecting from the very bottom of the tank the polishing system is even more effective in removing water and crud.

 

[pcatterall]

I still maintain that it only gets one pass!! If you start up and there is loads of gunk in your tank this will pass through your filters and whatever is not filtered out will go to your HP pump a portion will go straight to the engine and the rest will be returned to the tank.

 

[Marsupial]

I still maintain that it only gets one pass!! If you start up and there is loads of gunk in your tank this will pass through your filters and whatever is not filtered out will go to your HP pump a portion will go straight to the engine and the rest will be returned to the tank, where it will go round the circuit again and again. its part of the design