Sludge in Fuel Tank

[Bassnailer]

Hello, I have dual fuel tanks, but have only been using one as the other had nasty, dark brown sludge the viscosity of thick cold honey in it. The tank is out of the boat, and I am wanting to put it back in. What's the best way to clean this tank? It's translucent plastic, and the guy at the parts store suggested diesel fuel, however after a day of soaking it really hasn't done much. The sludge will flow, sort of, if you move the tank around, just real thick. I've seen muriatic acid, drain cleaner, Lysol, dawn dish detergent, propyl alcohol and every other cleaner suggested on internet. I am leaning towards the drain cleaner, like red devil lye, about a cup full with a gallon of hot water. If I can dilute this stuff and break it up, I can go at it with a pressure washer. Pressure washer won't get everywhere in there though so I need a chemical which will mostly eat the stuff up without harming the plastic tank. Also, thought about taking to radiator shop and having it cooked. Thanks for any input, especially from someone who may have done this before. Oh, one more thing I know is always a concern, I am haswoper trained and there is a chemical bunker near by I can use to dispose of the caustic chemicals if that is the best way to go.

[92basshawk]

With old cars, Ive dropped a 1 ft length of chain in and sloshed it around and flushed. Rinse, repeat.......

[Bassnailer]

I've been working on this for a couple of days. Put Sodium Hydroxide (actually ZEP commercial drain cleaner) in at 1 cup to 3 gallons of water, swished it around, let it set a day, swished some more then drained, rinsed with fresh water, then dish detergent and water, and repeated. Also sprayed the pressure washer as much as I could through the small opening for the sender. I am getting some of it out, but I am not going to get it all out at this rate. Could really use some suggestions if anyone has any. Laquer thiner? Acetone? Any chemical I can put in this thing to dissolve the lacquered gasoline so I can flush it out? Pictures are where I am at now with it, after several days of attacking this stuff.

[Bassnailer]

Well, I got it cleaned out, and thought I would share what I learned. Sodium Hydroxide worked well to break down the sludge, although it did not get it out of the tank. Don't use ZEP crystals, as this product adds aluminum to the sodium hydroxide to produce heat, and then you also have to clean aluminium out of your tank. Use a pure lye product, like red devil if you can find it (I couldn't thanks to all the meth heads using it up). After you've given the sodium hydroxide a chance to work, rinse out the tank the best you can, I used a pressure washer but could only actually hit a small area. The pressurized water sill broke loose quite a bit of lacquer. Once I had rinsed it a few times, and the sodium hydroxide was no longer breaking anything down, I put in 5 gallons (24 gallon tank) of E85 fuel and a bottle of Heet. This sloshed around in the tank for the 12 miles from the station to home, and by the time I was home the inside of the tank looked new. The photo in the post above was after sodium hydroxide but before the E85. With all the sludge dissolved in the E85, I rigged up an auxiliary fuel pump with a fuel filter and circulated the fuel in the tank, sloshing it around from time to time to get the top and sides thoroughly rinsed. I circulated for about an hour, and went through 3 fuel filters. I filtered the fuel because I didn't have anywhere to go with the E85 once I was done and was going to just burn it a gallon at a time in my truck (it's flex fuel). I then pumped the E85 out, vacuumed the aluminum left over from the ZEP crystals, and had a tank which looked brand new. If I had this information it would have only taken me an afternoon to clean this sludged up tank and make it clean as new, so hopefully the next guy can benefit from this.

Sludge in tank before E85



After E85 with circulation pump set up