BMW E38 fuel tank leak and vacuum
Why does the E38 fuel tank leak?
The E38 tank is metal and often rusts on the top around the mounting bolt or at the seams of the lower edge. A leak can also come from the base of the filler pipe, which is a known fault. The holes in the tank are often pitting corrosion, and there are usually several.
Why does the E38 tank make popping noises and get crushed?
The cause is usually a blocked vent: the charcoal canister or the vent hoses do not let air through, and vacuum builds up in the tank. The tank is thin sheet metal, so the vacuum strains the seams and causes leaks. The canister is under the rear inner wheel arch liner on the driver's side.
Should you patch or replace the E38 tank?
Patching works, for example after sandblasting, but a rusted tank often has several leak points, so a patch is not always enough. The vent must always be fixed, otherwise the leak returns. Removing the tank is laborious: the exhaust, the driveshaft and the rear seat have to come out.