Tank Debris Question

boatmike

boatmike

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When I bought my Aquastar the tanks had been empty and dry for some time. Since I have had it I have had to clean the main filters regularly (too regularly in fact) So I have bitten the bullet and cleaned out both 450 litre tanks thoroughly. Due to them having 2 baffles in each I have had to cut two new hatches in addition to the existing to do it but it's now done. What I found was that the bottom of the tanks had a hard gritty residue clumped in lumps which in some places has corroded the inside of the tanks (aluminium) to a depth of up to 1mm. Now I have cleaned out diesel tanks before and had sludge but never this hard gritty residue. I am curious. Does anyone know what it is? Obviously the result of the dreaded fuel bug in some form or another but having dosed with Grotamar I think the bug is dead as the diesel siphoned off from above this crap is pretty clear. Also these particles are quite heavy and settle out in the bottom of a jar of diesel taken from the tank bottom quite quickly. Is it bug poo? Is it bug corpses? Some by product of the bug? I am pretty sure I have got it all out and disposed of it but having never seen the like before I am curious.... Anyone else seen this? It looks and feels more like sand and fine gravel than sludge.... Any chemists or fuel technologists out there know the answer? Could it be biological residue that has hardened while the tanks were dry? I posted in PBO forum but didn't get any useful replies....... anyone here know?
 
That's a logical conclusion Simon but if you saw the quantity its just not credible that this volume of crud would get in during refuelling and as its a 1990 vintage boat I can't imagine it was always there. Each of the 450 litre tanks had enough of this stuff to settle out about 2 ins deep in the bottom of a bucket when pumped out. It isn't sand or grit either because it crushes down to a fine powder when you squeeze it between your fingers. My guess is that the previous owner drained the tanks and left a residue of contaminated fuel behind which has been exposed to air and dried out in lumps. That's just a guess though...........
 
It could also be corrosion products if any iron debris had got into the tank (galvanic corrosion ).
 
It's not salt by any chance? i.e. previous salt water contamination Also aluminium can corrode to form a white salt in fuel systems. Had lots of issues with that in old ali based carbs before.
 
The ecretia from diesel bugs will eat aluminium that's why aircraft fuel tanks are rubber lined.so you probably have corrosion products salt and dead bugs. Check that you have sufficient tank thickness left where it has corroded.
 
Yes. I have a 4mm thick tank and no corrosion is more than 1mm. I have obtained a high performance epoxy that I am assured is diesel proof and have "repaired" the worst patches anyway. Thanks for your input.
 
The other thing I forgot to mention is this - Diesel fuel is made from refined crude oil. In the refining process the crude oil is heated and treated with chemicals that help break apart the long carbon chains. These shorter chains are then passed into condensing units, which stratify into different levels of fuel. One of those levels is diesel fuel. Because fuel nowadays is so valuable additional chemicals ( called catalyst cracking) are added which help to produce more diesel fuel from the crude oil. Because of this process the fuels are very unstable and start to quickly revert back to their original form. This process is known as the repolymerization of middle distillates, and can start as soon as 30 days after refinement. In other words the fuel has already started forming solids long before the fuel is delivered to the retailer.

So much of what you find in the bottom of the tank will in large part be due to this. Regular tank cleans is the only practical recourse, the periodicity of such cleans would have to be found from experience - but in a 2 tank system not a bad idea to do one tank a year until you establish the rate of deposition. Run your onboard fuel down to less than 50%, transfer over to one tank and clean empty tank out. Clean the other tank the following year. It is not the most pleasant of jobs and in some boats it is barely practical and may involve removing the tank. In the latter case visual inspection using a USB camera may inform the next steps.
 
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I have this in my petrol tank, a fine sandy grit, keeps getting through the filters and clogging the carb. It's driving me nuts trying to resolve where it's coming from. This also disappears into powder when rubbing. My tank is stainless and has 60 gallons of fresh supermarket petrol with a stabiliser added and new fuel lines, but it still appears.
 
NormanB said:
The other thing I forgot to mention is this - Diesel fuel is made from refined crude oil. In the refining process the crude oil is heated and treated with chemicals that help break apart the long carbon chains. These shorter chains are then passed into condensing units, which stratify into different levels of fuel. One of those levels is diesel fuel. Because fuel nowadays is so valuable additional chemicals ( called catalyst cracking) are added which help to produce more diesel fuel from the crude oil. Because of this process the fuels are very unstable and start to quickly revert back to their original form. This process is known as the repolymerization of middle distillates, and can start as soon as 30 days after refinement. In other words the fuel has already started forming solids long before the fuel is delivered to the retailer.

So much of what you find in the bottom of the tank will in large part be due to this. Regular tank cleans is the only practical recourse, the periodicity of such cleans would have to be found from experience - but in a 2 tank system not a bad idea to do one tank a year until you establish the rate of deposition. Run your onboard fuel down to less than 50%, transfer over to one tank and clean empty tank out. Clean the other tank the following year. It is not the most pleasant of jobs and in some boats it is barely practical and may involve removing the tank. In the latter case visual inspection using a USB camera may inform the next steps.
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Interesting post, thank you. In my case with two tanks with a total of 900 litres removing the tanks is close to impossible. They are built into the middle of the boat and just to get access to the top requires removing furniture and floorboards which is a major work up. They have been there since the boat was built in 1990 and because I have had to cut hatches to gain access to 2/3 of the tank due to baffles the build up of crap in there is over 26 years so in this sense understandably bad. Accepting your explanation which seems entirely credible I am inclined to think the problem was made considerably worse by the previous owner draining the tanks and leaving a sludge in the bottom for 2 years which exposed the toxic mess to atmosphere over a large area which probably created a lovely "garden" of hydrocarbon for the bugs to feed on. In fact the corrosion was entirely confined to the tank bottom and there is none at all up the tank sides which would support this theory.
Having cleared all this crap and run the remaining fuel through a 10 micron filter three times now with virtually no contamination showing on the filter I think I may be OK. I certainly hope I don't have to go though this every year and have never had to before over my 55years of boat ownership. If the boat is used regularly the normal action of flow and return on a diesel engine helps to polish the fuel. Its stagnant tanks that get little turnover that are going to suffer the worst. So I agree that monitoring the situation on an ongoing basis will identify any need for future action. Without getting into comparing trade names, there appear to be two types of fuel additive I could now use. One is the enzyme treatment which is said to "digest" contamination and the other are "bug killers" which are said to poison the bugs off. As you appear quite knowledgeable regarding fuels, which would you think most appropriate to treat the remaining fuel I have?
 
wheelie said:
I have this in my petrol tank, a fine sandy grit, keeps getting through the filters and clogging the carb. It's driving me nuts trying to resolve where it's coming from. This also disappears into powder when rubbing. My tank is stainless and has 60 gallons of fresh supermarket petrol with a stabiliser added and new fuel lines, but it still appears.
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Quite simply the crap is lying in your fuel tank and wont go away. New fuel lines and filters won't solve it. You have to clean out the tank. If it's not too large you should consider removing it and cleaning it out. If it does not have an inspection hatch I would seriously consider cutting one. Before you do though remove all fuel and fill it up with water. Otherwise it might well go bang!
 
Cutting Petrol tanks is risky.

In the Motor trade I have heard of quite a few nasty injuries from Fuel tank repairers, even with water filled tanks!!

I used a wet vac in my tanks, and with the brush fitting managed to scrape and vac most of the crap out. Not perfect but as good as needed to take the tanks back a few decades!
 
Whilst I haven't suffered the build up of detritus in my tank that the OP has suffered I was finding debris accumulating in the Racor filter. It turned out the copper pick-up tube was being 'eaten' and sending the resultant gunk up the line. A new steel pick-up has solved the problem. So no matter how well you have cleaned the tank, don't forget to check the pick-up too.
 
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