ok first off, how big are the tanks in the 1995 model 520i's
my display reads 80L but when i fill up i only put in about 60, unless it has an AWEFULLY big reserve.

my fuel consumption is 18L/100 on average which equates to 15miles/gallon

why is my fuel consumption so bad? its worse than the v8's driving round town . any help would be very useful. thanks

oh and i used a fuel additive to clean out the engine but did not help much

i also dont use the cheap fuel. i use middle of the range octane 95 i think it is, as opposed to octane 92

whats the first things i should check/do