I had three tanks that were so bad I was going to toss them. One was from a 79 R100RT with only 4800 miles. The owner had parked it with 1/4 tank of gas in 1986 and never touched the bike since then. The fuel cap needed to be drilled out as the lock was frozen solid. The interior was rusty, crusty and dee-scustin'
The 2nd tank was a 1985 Yamaha FJ1100 tank with only 1900 miles. Also parked for over 30 years with fuel in the tank. The fuel had turned to goo. After removing the fuel cap hinge (the locking cap was frozen), The tank was rinsed out and the big chunks removed. After it was dry, it still had chips and things moving around inside.
The third tank was a Meier Sporttank from a /2 which had been parked against the side of a house in Mendocino (Northern California coast) for more than 15 years.
I treated the Meier first. The 5 gallons of ER filled the tank so minimal sloshing was needed. I left it in there for 5 hours while I did other things. I used the rusty petcock to keep the tank sealed. It was going to be replaced anyway. The ER was drained back into the original pail and the tank rinsed with water. The interior looked amazing. The tank walls were like smooth gray metal with various lingering spots of rust, certainly good enough for an few cleanings, an acid etch and coating with Redkote.
Next up: the RT tank. Part of the experiment was to see how many tanks the ER could handle before it lost its cleaning power. The instructions say that the liquid will get darker and darker as it removes the rust. The chemical process (which I do not fully understand) apparently converts the rust into carbon. Part of the carbon is absorbed into the liquid and the rest stays on the surface of the part to be rinsed off later. I left the RT tank for 2 days. It, too, came out remarkably well. There is some light patchy surface rust inside which I may attempt to etch, since it is getting a redkote too, but all of the super crusty chunky rust is gone.
The FJ1100 tank was the worst of the bunch. I had actually bought another tank on ebay because I had given up on the original one. However since the bike only had 1900 miles on it, the paint was perfect so I really felt bad about trashing the original tank. The ER was quite dark after doing the first two tanks. So I left it in the FJ tank for a week. The tank condition went from "trash it" to "usable". Not perfect. But certainly usable. All the loose rust washed away and the remaining surface was gray metal with patchy surface rust spots. I will probably use caswells on this one as I like it and it does not need to be redkoted.
I poured the ER back into its pail, thinking I might get a few more uses out it, or I might be able to let some smaller parts soak in it. When I get another rusty tank, I'll buy another 5 gallon pail.
The ER instructions say that , once the ER turns dark, it is fully biodegradable and safe to dispose of down the drain. They say it is safe to get on your skin too. That was one of the things I was attracted to about it.
It comes in quart and gallon containers too. Give it a shot. I think you'll be impressed.
I am in no way associated with Evap-Rust. Just a happy customer.
Scottie's Workshop, Santa Clara CA
Full Service repairs, maintenance and restoration workshop for vintage and classic BMW Motorcycles http://blog.scottiesharpe.com
92 R100RT/69 R69S
2004 Aprilia Atlantic 500cc single cylinder Scooter
83 Honda V65 Magna, fastest production bike in1983