Mooch 4/8/2011The tank vent is clogged. Spiders cam get up in there and their webs keep the tank from venting properly.
txmarshall 5/27/2011Don't really know much about Mercedes Benz do ya Mooch? gamsta... Your 500 sel's fuel delivery system in designed to hold a certain amount of pressure in the tank and fuel lines when it's not running.It helps the engine start faster when it's cold. the electric fuel pump delivers fuel at around 80psi to the engines Constant Injection System (fuel injection system) but it uses about 35psi so the extra fuel is sent back to the tank under pressure via a return line creating the needed pressure in the system. Relax.... Your baby's just acting normal!!