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2003 BMW 330i gas mileage dropping

So as stated, I have a 2003 BMW 330i. It has about 92K miles on it, and I just did the 90K-mile inspection. Just before the inspection, the transmission (automatic, with steptronic) died, and I had it rebuilt, and I haven’t had any other problems until (maybe) now.



A few days ago, I parked on a hill, so I engaged the parking brake. When I came back, I disengaged it (or so I thought) and I drove home (around 10 miles). The next day, I drove it again, but I soon realized that my gas mileage was below normal, and I instantly though about the parking brake. I looked, and it was about a third of the way up…not all the way down, but also not far enough up to cause the parking brake indicator to light up on the dashboard. I’m not even sure if it was having any effect. I disengaged the parking brake all the way, thinking that would fix the problem. To see if it fixed the problem, I reset my MPG gauge on the dashboard.



Normally, for city driving (around Rockville, MD/DC area), my MPG hovers between 22 and 23 MPG. After I reset the computer, I was still getting pretty low gas mileage. At the end of the day today, the average MPG was between 14 and 15.



My roommate just took the car out to see if there’s anything obviously wrong with it, and he says that it’s not the transmission (which is a relief). Does anyone have any idea what it could be?

The major issue I would be concerned with is an overheating transmission. Did the cause of your transmission going bad ever get discovered? That is real rare for any BMW to need a transmission at 92K.

You are going to have to step back in technology a bit and do a normal “how far I went divided by how much gas I put in” measurement to see if it is the indicator that is wrong. Do keep your eyes, ears and nose open for anything out of order, this early transmission repair concerns me. It is equaly strange you actually found someone to rebuild your transmission,this was always a replacement item not a rebuild item,who did the rebuild?

Yes…the repair shop said the cause of the transmission problem was a broken O-ring or something…I don’t remember off the top of my head…my parents took care of it because I’m living and working in MD and the transmission broke while it was down in NC. I actually bought the car used (with about 80K on it) and the mechanic said that the transmission problems may have been caused by the driver (probably the previous one) not coming to a complete stop before changing gears (i.e. from reverse to drive). Actually, don’t take my word as gospel about the O-ring…I’m asking my parents now about the details on that one.

I’ll take a look at the math on the MPGs…I hope it’s not the computer that’s broken…I hear that can be expensive.

Average MPG over a short distance is not very accurate. Give it some more time(miles) to allow MPG to give a more accurate reading.

I was thinking that, but my original concern came when after averaging 22-23 MPG for a couple of months, that number dropped under 20 within a day and a half. I will give it a few more days and see what happens though.

Jack up the rear wheels and spin then by hand in neutral, if they spin freely, your emergency brake isn’t sticking.