The International Cessna 170 Association

I am sure this has already been covered but I need some advice. After removing my left fuel tank which was seeping fuel down the wing and out the flap, I pressurized the tank and sprayed soapy water around the drain I found two pin holes. I also noticed bubbles from a suspected pin hole I could visually see. I took it to a local shop to repair the pin holes. When I picked up the tank this morning The welder told me after they welded all the areas I had marked they pressurized the tank and submerged it in water. He then told me the tank was leaking everywhere, looked like a sponge leaking air out from all over the bottom. We had discussed a lot of little blue fish eyes which were visible after I cleaned the majority of the fuel stains off the bottom of the tank as to they might be additional leaks. Turns out that was true. So, the tank is un-weldable to repair. Is there a recommended procedure and product to seal the inside of the tank or must it be replaced?

Sounds like a set of long range tanks I recently bought described as having a dent and a hole

As my mechanic who is a certified welder said; Anything is fixable but is everything worth fixing?

There is no approved method that I know of to seal a corroded tank as you describe and my experience with tank sealers in motorcycles tells me to never try it on an airplane.

Fortunately, the tanks are fairly easy to come by in junk yards as they are the same as the early 172 tanks.

I have some stock tanks if you are interested. Long range can be an expensive adventure pM me if you are interested. Shipping might be a bit expensive compared to down south as I am in Alaska. If you are near where Alaska Airlines flies in General freight is not bad and I am a known shipper

Sloshing sealers have been used in ground-bound vehicles but I'd not trust them in aircraft. As already mentioned, lots of tanks are available salvage, and Wag Aero and Univair sometimes have N.O.S. tanks.