D5 – Crud in the Fuel Tank

by Steve Finberg

As much as it surprises most U.S. mechanics, the Limeys painted the insides of our gas tanks! This paint is now starting to flake off (at least on my 3 cars and several others in New England). Don’t get me wrong, I am not complaining. Everyone with whom I have talked thinks paint would not last a few weeks in a gas tank, let alone more than 15 years. In fact, the paint is not dissolving but rather is losing its affinity to the metal. The paint flakes off and tends to clog the cross pipe to fuel line connection. This can lead to many confusing problems, but primarily it results in gas starvation. Before the line is totally clogged only a trickle can get through. This may be enough at idle or around town, but can lead to overheating or stalling at speed as the carburetors are forced to run very lean. Eventually the line will clog completely, either at the cross pipe or at the fuel pump. I have seen a fuel pump changed only to have the problem reoccur in a few weeks.

In an Alpine, the first sign of a problem will be the small black curly flakes in the fuel pump bowl. However, this is not where the system usually clogs. The clogs occur at (1) the right angle inlet to the fuel pump (fixed with an in?line gas filter), (2) at the junction of the gas line to the cross pipe at the gas tanks.

The blockage at the fuel pump can be cured by removing the fuel line and pushing out, with a small wire, from the pump bowl. The blockage at the cross pipe can be cured only temporarily with compressed air, by blowing it out from the fuel pump end. It will generally return within 10 to 20 miles. A slightly more permanent fix requires removing the gas line at the cross pipe and pulling the crud out with a hooked wire. Be prepared for a slight trickle of gas as the line is first removed, and a major flood as the blockage is removed.

Unfortunately this is only a temporary fix, as the paint flakes off slowly and will block up again sooner or later. Watch the filter for first signs. It seems to clog sooner in the summer than in the winter.

A permanent fix requires removing the fuel tanks and stripping off the inside paint. This is easier said than done. My first approach was to take the tanks to the local radiator shop. The owner assured me that one day in his tank would rot out any paint completely. A week later, only about 80% of the paint had been removed, the rest looked slightly flaky. He didn’t think much more would come out, and I think he wanted the space back. Next I tried several paint removers and solvents available in my lab, but none even touched the stuff. Finally, I took a length of sharp edged window sash chain and shook it around inside the tank. A thorough shaking removed the rest of the paint. I then washed the tank in water to remove the loose flakes and dust, and any remaining radiator shop fluid residue.

A thorough inspection of the tanks and cross pipe (with paint removed) revealed several pinholes, which may have been blocked by the paint. I brazed them shut. The exterior was then wire brushed, primed and painted gloss black.

In the week between the washing and the planned installation, the tank showed some slight rust. I decided to coat the inside with “Hirsh” gas tank sealer, as advertised in Hemmings Motor News. It is advertised for coating rusty antique gas tanks, and supposedly seals any rust and plugs pin holes. It is a yellow, very sticky paint, which, when applied and sealed in a tank, exerts quite an outward pressure, forcing it into any pinholes or seams. The company assures me that it will not flake off or dissolve. As I have just finished so I cannot yet report any results.

A convenient time to inspect the wells for accumulated dirt and rust, and to restore the inside paint is while the tanks are out. This makes body work in that area so much easier.

To get around temporarily while the main tanks are out, a marine tank can be connected to the fuel pump or filter. An inexpensive one for this purpose is the Sears Game Fisher Tank.

Editors note: The gasoline in the fuel tanks should be siphoned out before cutting or disconnecting the main fuel line to eliminate draining gasoline on the ground or your garage floor.