Drop in fuel economy mpg, possible odor of gas

[iploya]

For the life of my 325i (85k miles) my fuel economy (mpg) has consistently averaged in the mid 21s. I reset the gage every time I fill up, and it usually converges pretty quickly to around 21-22. My daily routine is about 80/20 highway/city.

About a month ago, I noticed several times where my average mpg on the digital display would be low, like in the upper 18s or lower 19s. I wouldn't actually see the change happen on the display - more like I would glance down after starting the car or after having been driving around and notice the low mpg. I'm sure I glance at it several times per trip.

Around this time, there have also been a few occasions where I notice the odor of gasoline, or what I assume is the odor of gasoline. Yesterday I fueled up in the morning, did quite a bit of highway driving, some city driving (my usual routine), and when I parked the car for the evening I was down at around 18.9mpg again. I got low and sort of sniffed under the car and detected the odor of gasoline. Again, maybe I am mistaking another smell. But the combination of gas odor plus randomly dropping mpg suggests to me a leak somewhere in the system.

However, I just brought my car in this morning for a thorough visual inspection, and they found nothing. They said they had it on the lift, checked all around the tank, engine, and even removed the cover to check the fuel injectors. They gave me the keys back and said there's nothing else they can check for.

Any ideas what else this may be? Perhaps I'm just mistaking another odor for gas, and just getting some odd mpg readings for no reason, but I'm not giving up on trying to figure this out.

[Mima]

Did you do check all the basic fuel mpg tidbits? (ie. proper tire pressure, air filter, change the fuel source or octane rating, did you ever change the oxygen sensor etc.)

[mattjw916]

Does the gas cap seal properly? Any visible signs of a leak? Fuel lines are pressurized so if they were leaking they'd probably be spraying fuel. If there was a leak around the fuel filler neck the smell would substantial. Climb under and poke around.

My 325 dips into the teens (18, 19, but usually is around 21) for lots of city driving so I'm not totally convinced you have a tangible problem. g/l

[I Love My E36]

I actually had this problem with my 325 as well. removes you back seats (bottom part)
and check if the plastic cap isnt broken. remove the black cover with the 4 screws and once you see the 2 hoses, a "thin one" & a "thick one", turn on the car to see if it starts to leak. if not, you might want to lift the car to see if there any other leaks

[cazzman]

I have had similar problems but decided to do manual calculations from tank to tank. Dont always trust computer. Sometimes 2-3mpg difference

[mryakan]

I have had similar problems but decided to do manual calculations from tank to tank. Dont always trust computer. Sometimes 2-3mpg difference
You do not trust the computer but trust the inaccurate pump at the gas station? Do you know that the computer on these cars measures exactly how much fuel it is feeding into the engine and uses that in its fuel consumption calculations? How can anything be any more accurate than that!!! Your calculations do not take into account fuel that evaporates and escapes while filling up or variances in how much gas the car takes before triggering the shutoff valve on the car, or even inaccuracies in the pump measurement itself (how accurate is that afterall and what guarantees do you have they did not cheat you intentionally or unintentionally out of a portion of a gallon).
Be sure to reset the mileage calculation after every fillup to get a current meaningful average and wait for more than 10 miles before it settles on an average that reflects your driving.

[kauaiboy]

i too have an 06 325i and have been averaging the most 28mpg...i've noticed before that if i don't use chevron premium grade fuel, my SES light would come on so i always use chevron...i bought the car with 76K and it has now 83K...

[cazzman]

@mryakan point taken, and agree with your comment, happy driving!