Um, I have a 96k 530i 5spd manual and am averaging 29-30.5 MPG on the highway. I've been driving it from Tampa to Pensacola and back every week since I got the car almost a month ago. I've been averaging anywhere from 27-30.5mpg on the highway. 22-26 MPG around town. Thats on 87 and 89 fuel with some crazy driving. On 89, doing 80 I pull 29.0. with 87 I get 27.5. Manual trans oil is original, on my list to replace soon. O2's are original and the fuel filter is original. I did cooling system, plugs, tires, alignment and diff lube when I got the car 3 or 4 weeks ago with 93k. My recommendation would be to change out the diff oil with 75/90 Mobil 1 or another 75/90 Syn GL-5 Gear oil of your choice. Our cars are open diff, special oil is not required. When I did my diff oil the original stuff was toast. Let me repeat that, TOAST. And for some reason a lot of manufactures and people like to run the 75/140. News flash. We have 225 HP. 75/90 synthetic is more than adequate and more MPG friendly. 75/140 is more warranty friendly for reduced idiot failures.
On a side note, my car revs too dang high on the highway. It needs a 6th gear. 3,150 rpm @ 80 is a joke. 2,500 or 2,750 would be ideal for just cruising.
EDIT: for reference my 335i is getting about 27-29 on the highway. Low 20-24 around town. All on 93 gas. SO my 530i is older, bigger, heavier and more fuel efficient. But i's missing two turbos and has skinnier rear tires.
DD: 2003 530i 5spd manual sport package. Conti DWS's, Llumar ATR, White LED lighting. TLC on-going.
Garage queen: '07 335i Sedan, base pkg, 6spd Manual, Procede 3 V5 w/NLS, staggered 18" 313's w/Conti DWS's, OS Giken TCD LSD, VAC Street Diff Cover, Akebono Euro Pads, CDV Removed, Black BMW Grilles, Interior & Exterior white LED lighting, LUX Angel Eyes, Debadged, Llumar ATR Tint.
Last edited by FLE39; 10-12-2012 at 10:58 AM.