VW - Fuel Tank, Rust and Filters

One bit of bad advice you'll frequently hear is to install a fuel filter in your fuel line between the fuel pump and the carb.

Don't do it.

The added mass of the filter combined with the vibration of the engine and road serves to wiggle the brass ferules out of the carb and fuel pump. When that happens if you happen to have some marshmallows with you, fine, otherwise there's little you can do but stand by and watch it burn.

Volkswagen used untreated mild steel for their fuel tanks. Because of the age of the typical Volkswagen, the fuel tank and fuel lines are generally quite rusty; that is the source of the residue you find in the carb bowl. Adding another filter (you already have two) deals only with the symptom, the real solution is to tackle the rust itself.

The factory service manual addresses fuel tank refurbishing in considerable detail but the real secret to success is what you do after you get rid of the rust, which is to use a chemical sealant commonly called 'sloshing compound.' You pour it in and slosh it around, then allow to dry. Be sure to remove the strainer first. This is some very tough stuff, used in metal fuel tanks on aircraft. It is available from J. C. Whitney.

A rusty fuel pipe is a more serious sort of problem since the location of the pipe within the central hump makes replacement difficult, best done when the body is removed from the chassis. I've mentioned another fix, the use of an externally routed replacement fuel line, in one of my earlier articles ('The Stainless Steel Craftsman').

Cleaning your existing filters and even adding another can buy you a little time but please do not install it within the engine compartment. Under the fuel tank is the safest place, followed by under the rear seat deck (ie, near the nose of the transmission). Veedubs love to burn; they're very good at it.

Your fuel system already has two strainers installed, one in the fuel tank, the other in the fuel pump. The latter is often overlooked as a maintenance item. On the late model pumps it is under the top cone, in early pumps it's behind the big brass nut. When you have a rusty fuel system you should clean the fuel pump strainer when you do your oil change. (But be careful, remember the fuel will flow by gravity once the system is opened.)

Rust forms in the fuel system due to an accumulation of water vapor from the atmosphere. When it condenses it collects in the lower-most stampings of the fuel tank, a depression around the fuel outlet fitting, where it produces pin-hole leaks. VW fuel tanks are not made of terne-plate (lead-coated steel normally used for tankage by American auto manufacturers) but are common mild steel sheet. Once liquid water is present in the fuel system it's difficult to remove without draining the tank through the filler neck (ie, up-ending the thing). As a general maintenance item the usual method is to add a 'dryer' to your fuel, as frequently as dictated by your local climate. Gas 'dryer' is nothing more than wood alcohol (methyl methanol?) and is available at any auto parts store. Being hygroscopic, the alcohol mixes with the water and, if there isn't too much water, will be burned as fuel.

The water/rust problem is less frequently seen on veedubs fitted with the full array of pollution control devices, since the fuel tank is not vented directly to the atmosphere.

If your fuel tank is seriously rusted, the wiser course is to replace it rather than repair it. (I'll pause here and wait a minute until all the weldors stop rolling on the floor with laughter.) Replacement fuel tanks are available although the workmanship is rather shoddy; they often arrive already rusty. If you buy one it's a good idea to treat it as if you'd made it yourself, removing the existing paint, smoothing up the welds (bloody dangerous!) and repainting it with a high quality epoxy. The interior should be sloshed as a matter of course. Serious rebuilders have their new or repaired fuel tank powder-coated, which bakes the enamel to both the interior and exterior surfaces. The super-serious (and wealthy) have a new tank fabricated from stainless steel or aluminum.

Working on the fuel tank is one of the easier tasks of VW maintenance (at least, on a bug :-) since it is so accessible, held down with just four clips&bolts, and at waist level. (This isn't true for '68 and later models; the filler neck is especially difficult to re-seal.) Be sure it's empty before working on it -- six pounds per gallon can make a heavy load -- and that you have new fuel line on-hand. The existing fuel line under the tank will probably break like a stick when you try to disconnect it. (Lift one side of the tank, peek under, reach down and wiggle it loose.)

Pulling the fuel tank also gives you an opportunity to remove the fifty pounds of sand & gravel that accumulates on the 'smuggler shelves' behind the wheels when you take the short cut between San Ignacio and La Parisma.

Copyright © 1995 Robert S. Hoover