Well my 2005 2.5i was getting 16 mpg city and barely getting 24 on the highway! Something had to be wrong. The dealer said everything was fine. So with some research I found that there have been a lot of reports about the Vanos seals failing in this vintage 6 cylinder engine, found a fellow who supplies replacement seals ($60) and rolled up my sleeves.

After disassembling the Vanos unit the two pistons were literally flopping around in their bores...and the o-rings underneath the seals were as hard as ABS plastic!

After a short break-in period with the new seals I'm getting 19-20 mpg city and 28-29 mpg highway!!

Cheers,

Steve

P.S. BMW will replace the whole Vanos for you for $1000+...and the new one has the same crappy seals in it!!

What are the symptoms for bad vanos seals other than poor fuel economy? Also, how many miles does your X3 have on it? Thank you for posting this information.

The first symptom I noticed was a lack of low end torque. I felt I had to really put my put into it to get going. Another symptom was on a hilly (Vermont) highway in cruise control the car would hunt and kick down more often. Then I started noticing the mpg falling. I had done the Vanos fix on my old E39, so I checked on my engine too...and yes it had the exact same Vanos. The obvious symptoms started at 70K miles...but from the condition of the seals I'd say they were toast well before 50K miles!

The difference in pick-up is amazing...

Steve

my x3 gets horrible milage but probably because i drive with a heavy foot. sometimes it feels slugish and sometimes it hauls ass. do you think its the seals in the vanos like you said? it only 30k miles (48000kms) on it and its going back for end of lease soon.

I've heard that the seals start breaking down by 15K miles! Then I guess they progressively get worse.

Apparently the computer does try to adjust as you go so it probably masks the problem for a while. Another interesting thing I noticed after the repair was that while the mileage went back up almost immediately it took a while for the computer to re adjust to having good seals...so I felt a nice improvement in power right away...and the a few weeks later I started feeling a bigger secondary boost!!

Since your car is due to go back at the end of the lease I don't think I'd invest in the repair. It's not real hard to do, but it is time consuming and if something breaks you'll be spending time and money on someone elses car! I'd say it's a 4-6 hour job. I went very slowly...and I replaced the valve cover gasket and plugs while I was in there.

-Steve