We attend many BMW’s that have been misfueld, mostly 5 series, the 5 series has a complicated fuel tank set up, in that it uses a “saddle bag” design, which is the tank hangs over the propshaft, which makes it 2 tanks joined by a pipe at the top, and elaborate pumping system to keep the levels equal, this dual fuel tank system with pumps to distribute fuel evenly was pioneered by concorde in the 60’s, because the engines burned fuel so fast, gravity alone would not keep fuel tanks equalised , bmw, audi, landrover, mercedes are among the cars that are using it, the reason is to cram awkward shape fuel tanks around prop shafts, exhausts, etc
Draining the fuel from a BMW involves more than emptying the tank with a suction kit, there will still be half the fuel left in the other side of the tank, to get to this you either have to bypass the cars internal “brain” and turn on the transfer pump, or you have to lift out the backseat and access both parts of the tank from above.
BMW’s sometimes signal a fault code after a misfuelling, this is normal and is the engine management computer is simply saying “engine dont work” which you already know by the time it comes on. this is not usually an indicator that something has gone terribly wrong, nor has it detected wrong fuel as the cause of the problem, once the car has been drained and filled with the right fuel and restarted, the engine management light will go out.
No permanent harm is caused by a brief misfuelling, so don’t get taken for a ride by a dealer who suggests a multi thousand pound engine and fuel pump rebuild, its just a scam that is peculiar to the UK, BMW main dealers in Germany simply recommend a fuel drain and wouldn’t dare try and pull the new engine/fuel pump trick that our dealers have been doing.
Call us if you need help with wrong fuel, a fuel drain, or advice on how to do one.