I actually used Red Line in my 530 recently and got a 1.2 MPG improvement with city driving. I run 89 octane as indicated on the fuel tank cap. Prior to putting the bottle in a full tank I had been getting about 18.2 in the city with modest driving. My commute to and from work is roughly 50 miles. I put a whole bottle of Red Line Injection cleaner in my last full tank and noticed my MPG dropped by 1 - 1.3 MPG to 17.1. I've since filled up again and have been getting 19.4 halfway through this fillup. Whereas I had been getting about 80 miles per quarter tank, I am now getting 90 miles per quarter tank. I don't know if this is typical but I used to use it in my M30 E28 and my M20 E34. This was my first time using it in my M60.
BMWCCA Member #330940
Bayou Chapter, Louisiana