kongse

Hello all -
I have a 2008 550i with just over 70k miles. Starting at around 60k miles, I began knocking off a lot of maintenance items: new plugs, transmission fluid flush, in-tank fuel filter, air filters, rotors / pads, brake fluid flush, rear diff fluid change, PS fluid change, as well as refreshing some suspension components - front/rear shocks, sway bar links, control arm bushings and more. Car had three alignments over the last 10k miles as well. I always change the oil at 7.5k mile intervals with BMW synthetic.

After getting all this work done, my gas mileage has steadily plummeted over the last 10k miles. Whereas I typically would get 18-19 mpg in 50/50% city/highway driving, I am now routinely getting 10-12 mpg (using the car's computer as my gauge). I can't detect any loss of power or strange issues that would lead me to suspect anything else.

My tires (Michelin Pilot Super Sports) are grinding down to about 18k miles so will need to be replaced soon. I'm sure that's having a drag on mileage, but I find it hard to believe it's having such a dramatic impact. Tire wear looks fine.

Two mechanics have just shrugged when I've brought up this issue (I suspect no one wants to tackle an issue like this). I don't even know where to start on this one ... anyone have any suggestions or feedback? Much appreciated

BrandonSS

Have you calculated it yourself? I wouldn't rely on the computer. I typically get 280-350 miles per tank depending on Highway use. Miles on full tank/gallons to fill up =mpg

kongse

Yes. The computer is higher but consistently higher (3-4 mpg in my case). Getting the same delta between calculated and the computer mileage before and after the drop. The figures I've described above are the computer-generated ones.

psam550

Hi Kongse,

I have driven 2006 550i for about 6 years and consistently average about 18 MPG on mostly highway driving. (I reset my trip odometer every time I fill up and occasionally will divide the number of gallons purchased into the amount of miles driven on that tank). Have you been driving the car more aggressively since you started these maintenance items? (I drive more aggressively after I show my car TLC). If your driving habits have not changed, then I would double check the plugs and fuel filter to see if were properly installed/working and no fuel leaks. Otherwise, I can only corroborate that my 550i always gets about 18MPG. Good luck.

Psam550

Mike_08_550i_MT

I noticed, while trying to eliminate a shimmy by replacing front up and lower thrust arms, that both front calipers were not releasing properly. Jack up your car and check to see if the wheels spin freely. If they don't, it's time to replace the calipers and hoses. I just replaced the calipers on "meine Heidi" with Centric rebuilt OEM calipers off eBay and Otto's BMW parts desk hoses. They spin like a top now. Seizing calipers cause all sorts of havoc. BTW - shimmy = gone!


I did the work at 85k miles.

stoneisman

Hi,

My 2008 550i returns 18 mpg very consistently. I always calculate it by hand and ignore the computer. I will check it on my next fill up for entertainment however. My Highway trips I get 23 mpg which surprises the crap out of me given that I have 120k miles and a heavy foot but she loves to cruise at 80 and multiple trips have confirmed 23 mpg on strictly highway mileage for me. I haven't done nearly the PM you have except for the obvious tune up and big 100k service on my automatic transmission. The previous suggestions all have merit, but better is absolutely possible, even on a high miles 550i. Let us know if you track it down.

johnbennett103

You need to plug it in to check codes. I bet that you that your VANOs is shut down due to some error. With all the work that you have had done, the engine may not be put together correctly. I had an issue where my drivers side VANOS solenoids were switched, and my mileage fell from 18 to 14 mpg overnight, with a big loss in power. Once I found the error, I was good to go. Mechanics are only human(especially indy's), and they make mistakes.

e6t.lab.rat

1st try cleaning your MAF sensor and/or have it tested. Could be bad.

Any codes from OBD? A disconnected vacuum hoses somewhere? Bad PRV valves?

Just throwing it out there. Good luck