Cleaning a Diesel Tank

[Tim Mertinooke]

My ketch has a 45 gallon fiberglass fuel tank located under the cabin sole and I know that it is in need of cleaning. The access port at the top of the tank is one inch in diameter which is too small to be used to clean the tank, so I plan to increase it's size for better access. Assuming that I drain the tank of the ten gallons of diesel that's left in there, what procedures or chemical(s) should I use to get the sludge out effectively?

[LazyGuy]

I pulled my Monel tank. In hind sight, I wish I had put the 6" access plate in the top. The product that worked outstanding was "Marine Clean" by POR (Paint Over Rust). It is clear and you mix it 50/50 with hot water. The 32 gallon tank was clean (bottom of the tank was shiny) after 4 treatments of 1 qt Marine Clean (half gallon) treatment. What you pour out from the tank is ugly but water soluble. Allegedly, you can dispose of it in normal trash but i put it in the toxic section of the local transfer station.

Do you plan on removing the tank or clean in place?

[Tim Mertinooke]

The tank is fiberglassed into the bilge under the cabin sole so removal is impossible. It also has baffles which may complicate things. I will certainly check out the product that you mentioned. I recently heard that kerosene can be used to help flush out a tank too. Thanks.

[Hulukupu]

It was recommended to me by a marine diesel mechanic to repeatedly flush the tank with fresh or finely filtered used diesel. Depending on your access (I have a 6" access plate), one can either scrub the tank walls or use your pump to dislodge sediment as best you can. I used a large Mr. Funnel filter between fuel changes. I gave away the used fuel to a fisherman (who said he could use it for home heating) in exchange for use of his 12v fuel pump.