I'm experiencing some very poor gas mileage with my 2004 525i. Just for a quick overview the car has 86k miles and I've performed an oil change on it with full synthetic, has a K&N oil air filter that's brand new and has had the microfilters replaced as well. I reset the computer and took it for a very careful zen driving session to try and see what my MPG would be. As you can see it's a whoping 13.5 (air conditioner off)(tires checked and filled for proper pressure). It gets about 9-11MPG with careless fast driving.

I know for a fact this car has original spark plugs. Will it need a new O2 sensor? New spark plugs? What else do I need to look at to see what can improve the mileage? When I bought the car at 78k miles it was getting about 15-17MPG and now it's dropped severely, even with VERY careful driving. It has 20" rims on Nexen tires (TPMS goes off, but no worries all tires are fine, just bad sensor I need to replace after crushing it in an LA pothole).

It's worth mentioning that at idle if the AC runs it makes the engine quiet down, whereas if the AC is off the car rumbles more at idle. Any input would be appreciated, I'm getting tired of paying $200-250 a month in gas just to drive to work that is 15mins away.

I heard that the oil from the K&N filter can get on the mass airflow sensor(MAF) and cause it to misread to the computer. There is cleaner for the MAF at auto parts stores. Do NOT attempt to clean it with other solvents or some other device. It is easily damaged.

I also have an 525I and changed oil and spark plugs and mods etc.. My MPG is 17.5 it's a dramatic change from when i first bought it was 23 mpg. :confused: I'm also at 80k miles on my car too so i have no clue maybe your driving habits are causing the crappy gas mileage.

i have a 2007 530i and i get about 16mpg in the city, it's pretty pathetic and far off from the 20 bmw advertises. my car is healthy, too, and i drive it pretty conservatively. i just think bmw's get bad gas mileage...

My 2000 323i was getting like 12-14mpg once she hit 100k miles. The MPG gauge would never play, just chill at 12mpg lol. Through my experience with bimmers, higher miles=worse mpg.

Guys i too was getting shitty mpg and i had a friend recommend an oil that truckers use. I dont know if any one has ever heard of it but when i put it in my car my mpg shot up at least 5 extra. The oil is motorkote, you can find it at www.motorkote.com Check it out and after you use it let us know the results. It is a little pricey but my morning start ups are a whole lot smoother and my car idles better...

i think it's a really bad idea to use that stuff in an e60.

its actually an additive so its only like 16 oz of it you use and its rated top 5 additives in the nation..... Did you read the reviews? Iv been using it since last year and my car hasnt given me any problems and runs smooth....

yeah i know, i just don't trust oil additives. reviews don't mean anything to me if you find them on the manufacturer's website. do you really think the manufacturer would post someone that said, "this product is actually crap?"

You have a point but ................. iv been using it myself and im pretty picky as to what i use on my car cause i try to take care of it. I wouldnt recommend anything to anyone if i didnt use it my self and had great results. I know everyone is pretty hesitant on using new stuff but how are we suppose to find better products if you dont have people willing to use them to get honest reviews. Anyway, my car gained 5 extra mpg and the start ups are smoother and it idles a whole better..... Thats my review......