Drawing off some diesel to remove dirt from tanks - how much?

[DaveNTL]

Have two tanks with 300 litres each and I'm going to draw off some diesel from the sumps prior to getting a firm in to polish the fuel before a long trip.

How much would you suggest? Should I go and buy a large container and keep it for the purpose or would a gallon off each tank into and old engine oil container do?

 

[sarabande]

Have you been sloshing around the contents by being at sea in reasonably lumpy conditions recently ?

If yes, then I assume that any gunge is in the bottom of the tank. If not, then it's possible there's a rim of crud on the tank walls at the existing level.

In the latter case, you will need to dislodge the muck and dissolve it into the diesel. PBO tried out various treatment products: Marine 16 was the best IIRC. Stick it in the tank and agitate the contents ( ? air line, return supply pipe.... ?) Doing this will give the cleaning company a chance to deal with all the dissolved solids and muck.

I really cannot see that draining away, say, 5 or 10 l is going to do much in a flat bottomed tank. You cannot guarantee that the tank will drain down uniformly from the base upwards: fuel is likely to move in an inverted cone shape into the drain orifice.

In a tank with a sharply sloping base, it will be different; draining should remove any contaminated fuel evenly from the tap upwards.

Would it not be possible to arrange to drain through a transparent tube ? Then you can see when any mucky diesel is flowing through, and when it is clear.

 

[santelmo]

I have the same boat as you (nauticat 38) and I do this regularly after taking on some dirty diesel a couple of years ago. I drain off about a litre into a clear plastic bottle and sometimes get about a centemetre of dirt in the bottom of the bottle. If your tanks are like mine there is a cube shaped sump at the bottom where the drain cock is. Best to do it when the boat has been still for a while best of all when the boat has been on the hard. the dirt then has a chance to settle into the sump area. Ill PM you

 

[Piers]

If it's Fuel Doctor, they will draw some off for you - it is all part of their service. No need to do anything. And they will put it back all clean and sparking with no residue left in the tanks.

No connection to the company etc etc.

 

[DaveNTL]

Thanks for the replies.

As santelmo says, there is a sump with a slope aft (strangely if I move my fat backside forward the slope goes with me /forums/images/graemlins/smile.gif ) and drain lines with change over valves to a pump are provided from each tank.

So I am going to draw off some diesel but wasn't sure how much.

Anyone got any experience of Algae-X fuel treatment? Looks compact and easy. Far too easy to be effective I reckon. http://www.diesel-fuels.com/algae-x/magnetic-fuel-conditioning.html