View Full Version : Gas mileage!!! WTF HELLPPP

04-11-2012, 12:37 AM
Hey guys,

So let me start by giving a brief description of my issue.

My mileage is getting kinda high now, in the upper end of the 100k's and I have been getting horrible gas mileage for a while now. I have been avging about 13L/100km in my 04 320i, I dont know if the car thinks its an m3 or something, but that mileage aint right! I used to avg around 8/9 but now its getting ridiculous.

So now trying to figure out whats wrong, I've begun replacing things in order of ease and price.

I've changed:
Fuel Filter
Spark Plugs

What else is left?!

My engine is not burning a drop of oil, so im assuming its not blown. The car throws absolutely no codes related to the fuel mix (only throws code for 2 post cat o2 sensors which have been deleted for ebay headers, but i have now switched back to OEM Headers.)

Am I missing something?????

I've searched around to see if anyone has had similar issues, the only thing left on the list is Vanos really, I have not serviced it as of yet. Does Vanos affect fuel mileage that much? I'm guessing my Vanos has gone bad, seeing other threads saying after 70k Vanos is undoubtedly in need of service.

What is the site for those aftermarket vanos service kits that are supposed to be better than oem?

Thanks guys

04-11-2012, 01:15 AM
Get lighter shoes!

all jokes aside

Tire pressure
O2 sensors
air filter
look for vacuum leaks

If Vanos unit isn't making any noise I wouldn't worry too much about it.

04-11-2012, 01:23 AM
try measuring how far your actually getting to a tank and not the computers avg mpg, then start questioning

04-11-2012, 08:03 AM
To answer your question, a faulty vanos will lead to less power & worse fuel economy.

I would start off with addressing that if you haven't dealt with it yet.

Go here to order your parts. - The explanation is all there. Take a second to read.


04-13-2012, 08:09 AM
Cold weather and short trips definitely take their toll also. Have you changed driving habits? I went from 8 to 10.5L/100kms just because I went to very short trips in city and 0 highway kms.

If you're getting 13L/100kms on the highway...in a 320...then there's something very, very wrong. BUT, don't just throw money at the problem hoping it will resolve it. If your thermostat isn't closing, that will kill fuel economy, so will a 300lbs sub/amp in the trunk. Find out what the problem is first.

04-13-2012, 08:14 AM
Yeah, my 4.4 is getting about 9.4 l/100 and that's cruising at a steady 125 kmh. I'd ignore the computer and do a test with a full tank run it the refill tank and check the odometer to get another opinon. You're not smelling any gas around the engine or tank are you? Just trying to rule out a possible fuel leak.

04-13-2012, 11:38 AM
My 2002 325ci 5sd gets 7L/100km at 100kph, in the city, I get around 9-10L/100km depending on how I drive.
Some things to ponder...
What oil are you using? Hopefully BMW Castrol or Mobil 1 0w40.
Do you have an automatic or manual gearbox?
What tires do you have? wider, softer tires = lower mpg.
Have you checked each wheel to make sure it spins freely when spun? You could have a sticky caliper.
What fuel are you using? Non-premium fuel will reduce your fuel efficiency. So will using gas with ethanol in it. For best efficiency, use Shell 91. I think it's the only fuel in Ontario without ethanol. Ethanol has about 34% less energy than gasoline, so a 10% ethanol fuel will give you around 3% less efficiency.
Have you changed your oil recently?
Have you changed your engine air filter recently?
Has your car had its inspection II recently?
What is your tire pressure set at?
What's your mix of highway to city driving?
Have you checked for vacuum air leaks, especially in the intake boot/elbows? If you have never changed them, then you can pretty much guarantee that the intake is leaking. The dead giveaway is a whistling sound, but it doesn't always show up.
Here's some info to help you out.
Part #6 is the main culprit, though many of the smaller hoses can also deteriorate.

Here's what mine looked like