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Question DetailsAsked on 1/12/2016

How to solve sludge problem in a heating fuel oil tank. Tank is stored inside in basement.

Have had different recommendations and looking for any one who has had success with any one solution.

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2 Answers


Not something I would do indoors if avoidable - because of spillage likelihood and heavy odors from the cleaning. Best to have it taken out and cleaning solution cleaned outside (if light sludge) or taken to a fuel tank company shop for steam cleaning and inspection scope checking for interior corrosion if heavy or long-term sludge (because the sludge traps water at the bottom, causing rust).

Some tanks have a bottom drain below the fuel takeoff valve which will allow you to use the bottom drain to drain out water and sludge - though unless a sloping-bottom tank not much of the sludge will drain that way without tipping and sloshing it around to mobilize the sludge.

One of the best solutions - having a disposable cartridge fill filter (filtering the oil they are delivering to you) regularly using a fuel tank additive like Beckett Ultra Guard or Oatey Hercules Fuel Oil Sludge Treat in correct amount per instruction - add BEFORE tank is filled so is thoroughly mixed in as the new oil is filled.

Also, though this risks running out in an emergency, the more you let the tank empty before refilling the less sludge and water accumulation will stay in the bottom (assuming you are using at least a fuel oil dewatering agent) because the incoming oil stirs up the bottom material more, mixing it into the tank and then consuming it. Just topping off a tank,, while that gives you the best emergency reserve, leaves a lot of "dead" fuel in the bottom of the tank and at the end away from the outlet.

Another fairly effective method (should have been used by installer when it was installed) is to make sure the tank tilts very slightly toward the outlet end so the bottom and back end of the tank is not dead space which does not drain to the front. Less of a problem with indoor than colder outdoor tanks where the diesel sludges up in the tank when it gets real cold.

Note - if you are cleaning a tank in-situ, be sure to totally disconnect the fuel line to the appliances and any filter at that point, so they do not get crudded up with sludge. And last thing after the operation and refilling with the fuel, is drain a bit from any bottom drain to get any water or grit that ended up still in the tank, and also drain off a bit from the outlet valve before hooking the line up again to get any water or dirt that lodged in the valve.

Answered 2 years ago by LCD


Here is an article on handling fuel oil sludge problems which might help too -

Also, I would, in addition to using a fill filter (in addition to the filter which should be on the delivery truck), talk to neighbors about who their fuel delivery company is - you might be getting substandard product from them - either low quality product from the refinery or distributor, their storage tank is low or cold and getting sludgy, or there are some who actually mix in used motor oil and such to raise profits. What you receive should be free-flowing, have no visible sediment in it, not have water settle out if you fill a glass jar with it, and should be basically transparent/translucent (aside from the Solvent Red dye in it as rewired by law for heating oil which has not had the motor vehicle tax paid on it).

Answered 2 years ago by LCD

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