Technical Article

Fuel Tank Sloshing

(as appeared in the May, 2007 TSR)

By John Wright

Greetings All. Is it possible to have writer’s block if you only have to write 5 or 6 articles a year? I think so. Anyway, all I had to do was walk into the garage and was reminded of one thing that needs to be done to my TC this summer. The slight smell of fuel has been a problem off and on for years, and I think this summer will be the time I remove the gas tank for a good sloshing. I have done this to several tanks over the years having been first told about the process by Renk, back in the early 70’s.

The last tank I did was for an MGA. This special 22-gallon tank still had 3 inches of 40-year-old fuel that left a full inch of goop in the bottom of the tank when drained. This was very difficult to remove, and I tried a couple of things to dissolve it with not much luck. This stuff was tar and the tank must have been full of Sunoco 260 when the car was parked about 1967. Fresh gas did nothing, nor did Acetone, which was recommended by a chemist friend of mine. It might have worked if I was patient enough, but I ended up taking the tank to the local Redi-Strip. It took them a week of soaking to get 95% of the tar out. In the process, the welded in threaded insert for the drain plug dissolved too. Must have been made out of some alloy that the chemicals just ate up. Hopefully, you won’t have these types of issues with your tank, and it will be a much more straight forward process if and when it becomes necessary. If it’s as bad as mine, I would recommend having your tank boiled out by a radiator shop instead of a chemical process like I did.

I used Bill Hirsch’s alcohol resistant gas tank sealer kit. In the FAQ sheet, he says it will seal a tank that has rust inside and/or seam leaks or pinhole leaks. The goo must be removed first, and then he recommends treating a rusty tank on the inside with his rust remover. See his complete instructions for this procedure at: Click on the gas tank repair bullet and then the description of the product for a full question and answer page. Bill claims that his product is the only one that is alcohol resistant, which is necessary in this day and age with the ethanol in the fuel we use. Complete instructions are also on the can.

The process goes very quickly once you get your tank clean enough. If you are lucky and it just needs cleaning and not boiling out, you can probably protect your paint enough so as to not damage it. Use Hirsch’s or similar heavy-duty industrial cleaner if there is shellac or slight goo inside. Once clean use the Metal Prep or Gas Tank Etch as directed and rinse out. These chemicals will damage paint so be careful. Air dry thoroughly. Introduce the sealer and with all openings now duct-taped closed, rotate the tank all around to slosh the sealer into all areas of the inside of the tank. Pour the sealer back into the container from the tank. If this is a relatively low rust or rust-free tank then one application may be all that is needed. If you feel another application is necessary, wait 24-72 hrs. before pouring the sealer back into the tank to repeat the sloshing process. If you think the sending unit float may touch the inside of the tank, then put some Vaseline on the float when you reinstall it, otherwise the float may stick to the fresh sealer.

Total cost for me was about $150 which included the stripping, but I still need to paint it as it’s still in primer.

Another option is to use one of the gas tank restoration businesses. I used this service for a similar tank to the one I spoke of above. Same situation with the goo and rust. Their process involves cutting a big hole (which they re-weld back into place) in the side so they can get in there and scrape the goo and then sandblast the rust away. They also want to apply a thick coating to the outside of the tank that seals the outside as well. I was not enamored with the looks of this coating and the price was $400 for the job, which included new black paint. You would want to explore the options regarding the exterior finish of a T-series tank since it is not under the car such as an MGA’s. I do feel the end result was better than doing it my self as the tank is fully encapsulated and is guaranteed. The current cost of a T-series tank from Moss is $1153.