Okay, so I am putting a 98 ls t56 combo into my 86 Iroc and I purchased a plastic tank from a 99. I later found the pump in it to be junk as it was rusted beyond belief as the car had been sitting for smee time with barely any fuel in it. Anyways the tank has this brown sludge all over inside. It can be wipped out kind of if you pour gas or degreaser on it, but idk how I'll be able to get all of it out. Any ideas what caused this and something I can soak it in to wash it out. Also tried degreaser and a pressure washer and it didn't do much and I couldn't get to the top side obviously.

 

Could this be the liner? Did the plastic tanks come with one? It looks gray underneath so if gray is normal it wouldn't be.

 

No liner that I know of.

Technically, a laboratory test is the only way to know what the sludge is. However, educated guessing, someone filled up with Ethanol, "totaled" the car either mechanically or by collision. The car then sat in salvage for some time. While sitting the Ethanol pulled water out of the air then separated (ethanol solids/water settle on bottom fuel on top). The water rusted the pump and the fuel evaporated leaving you a nice little sludge.

You could buy a new (used) tank or try cleaning the existing, just a judgement call. If you clean and use the tank, I would change the fuel filter after a tank or two. To clean use gas (non-ethanol), or lacquer thinner.

 

Ya I'm pretty sure that's the case. Going to clean it and see how that goes.