[Bahooki]

I typically drive my car rather quickly about doing almost explicitly city driving, and average about 275-290 miles on a full tank of gas. My car computer averaged this at about 18.9mpg, and that was fine for me. Recently, however, I started to notice my distance/tank plummeting. It went to about 260 miles/tank, then 250 miles/tank. I figured my driving had just gotten a bit out of hand, so two weeks ago I forced myself to completely keep my foot out of the gas. In the past two weeks, I have not taken my car over 3,000rpm. I've driven in a high gear, cruising at about 1800-2000rpm usually. I also haven't gone over half throttle, with exception to a few steeper hills. Regardless of my conservative driving, my mileage continued to plummet. When I went down to 210miles/tank with this driving style, I figured something must be wrong. When I checked my computer, it told me I was getting 14.2mpg. This seems sudden and absurd to me. As of right now, I have 25miles to empty and have gone 167.2 miles on this tank.

I called BMW Northwest, and was told that it could be a "myraid" of reasons. Not a "myriad", but a "my-raid". To figure this out, I would have to pay for a $210 diagnostic. I asked if she could go into this myriad of reasons, and she told me she wasn't quite sure of the reasons. I then asked if I could speak to a mechanic, and was told "that isn't something we do around here.". I hung up.

My experience with cars tells me this is just my car needing a tune up. However, I still feel as though this doesn't justify the sudden continuous drop, and I haven't gotten any Check Engine lights. I'm not sure how my computer calculates my MPG, but I feel as though if it were a leak then it wouldn't be computed into my MPG.

Car is a 2010 E92 328i 6MT with 56,000 miles. I use Shell 92 octane.

Any thoughts?

[NOITALL]

Plugs and air filter.

[Ubersmooth]

My N52 is doing the same, in fact I've pretty much just been driving my 335i lately because it's getting better mileage. I just reset the throttle adaption, gonna see if that makes a difference. I had my rear main seal done and after the transmission was put back in, I noticed it's been shifting... Differently with worse mileage.

[floydarogers]

Try an indy - sounds like you're in the south part of King Co, or in Tacoma. Rolf's Import Auto Service and European Motors are in Lakewood, and Kassel Motorsports is in Puyallup. Indies usually are more open to speculation and generally less than the $210 you were quoted.

Been cold lately; perhaps the car hasn't warmed up properly, although the thermostat usually throws a code if it fails. Perhaps the tires have deflated in the cold weather.

There's a soldier at Ft. Lewis that posts under the name danielfast (might be on bimmerfest in the NW sub-forum) that has helped many people; might be worth tracking him down. Or go to an autozone or O'Reilly's and get codes read - especially the shadow codes.

[floydarogers]

Originally Posted by I'm wrong

Plugs and air filter.

Definitely check your air filter housing - mice may have built a nest in there.

[adidoman]

Winter gas blends effect gas mileage quite a bit, and it's usually cheaper in winter. I think the cold air has an effect as well. My car has dropped around 4mpg even after doing an intake cleaning in a n54

[floydarogers]

Originally Posted by adidoman

Winter gas blends effect gas mileage quite a bit, and it's usually cheaper in winter....

Seattle/WA State does not have winter gas AFAIK.

[Tom K.]

Don't know if they still do a winter blend change in MD, but I only notice about a maximum 1 mpg drop in cold weather mileage, which I mainly attribute to longer warm-up.

Tom

[fazman]

Originally Posted by Bahooki

I typically drive my car rather quickly about doing almost explicitly city driving, and average about 275-290 miles on a full tank of gas. My car computer averaged this at about 18.9mpg, and that was fine for me. Recently, however, I started to notice my distance/tank plummeting. It went to about 260 miles/tank, then 250 miles/tank. I figured my driving had just gotten a bit out of hand, so two weeks ago I forced myself to completely keep my foot out of the gas. In the past two weeks, I have not taken my car over 3,000rpm. I've driven in a high gear, cruising at about 1800-2000rpm usually. I also haven't gone over half throttle, with exception to a few steeper hills. Regardless of my conservative driving, my mileage continued to plummet. When I went down to 210miles/tank with this driving style, I figured something must be wrong. When I checked my computer, it told me I was getting 14.2mpg. This seems sudden and absurd to me. As of right now, I have 25miles to empty and have gone 167.2 miles on this tank.

I called BMW Northwest, and was told that it could be a "myraid" of reasons. Not a "myriad", but a "my-raid". To figure this out, I would have to pay for a $210 diagnostic. I asked if she could go into this myriad of reasons, and she told me she wasn't quite sure of the reasons. I then asked if I could speak to a mechanic, and was told "that isn't something we do around here.". I hung up.

My experience with cars tells me this is just my car needing a tune up. However, I still feel as though this doesn't justify the sudden continuous drop, and I haven't gotten any Check Engine lights. I'm not sure how my computer calculates my MPG, but I feel as though if it were a leak then it wouldn't be computed into my MPG.

Car is a 2010 E92 328i 6MT with 56,000 miles. I use Shell 92 octane.

Any thoughts?

I noticed something similar to this around the same time I noticed the first few drops in my driveway of the Mechatronic sleeve leaking (location of leaks is where the transmission shift is located when parked but closer to passenger side). Once the mechatronic sleeve was fixed and they topped up the fluid for the transmission i was fine again.

But if the mechatronic sleeve is done, you might as well do a fluid flush and new pan/filter as well in the process because the labor is all inclusive and all you are out is parts.

[Bahooki]

Originally Posted by I'm wrong

Plugs and air filter.

I'm off to check my air filter right now, thanks.

[NOITALL]

Originally Posted by Bahooki

I'm off to check my air filter right now, thanks.

They're cheap and running a clean filter gives you more power.
Plugs have a direct connection to performance and consumption. The sad thing on these cars is that it's actually easier to replace the plugs than the air filter hahahaha (not kidding).

[tuned2ride]

I never got better than city EPA mpg in my commute and for the same, I easily get the combined EPA mpg with our Civic. Even after air filter and spark plugs replacement.

[Bahooki]

Originally Posted by I'm wrong

They're cheap and running a clean filter gives you more power.
Plugs have a direct connection to performance and consumption. The sad thing on these cars is that it's actually easier to replace the plugs than the air filter hahahaha (not kidding).

I just took out my air filter and gave it a look. I wouldn't say it's trashed, but it's not in the best of condition. I just ordered a K&N replacement! It was a bit of a bear to get the hose that's connected to the MAF sensor off, but besides that it didn't give me too much trouble. Also, really?? haha, I'll probably have my local indy do the plugs. If it's easy enough, though, I might try it out myself.

[Bahooki]

Originally Posted by tuned2ride

I never got better than city EPA mpg in my commute and for the same, I easily get the combined EPA mpg with our Civic. Even after air filter and spark plugs replacement.

I've never gotten, or expected, to get the EPA rated mpg. It was the plummet that threw me off.

[NOITALL]

What's the EPA value for this car?

[Bahooki]

Originally Posted by I'm wrong

What's the EPA value for this car?

18 city, 28 highway.

[NOITALL]

Originally Posted by Bahooki

18 city, 28 highway.

Oh I get better values than these...

[Bahooki]

Originally Posted by I'm wrong

Oh I get better values than these...

Lucky...

[shuaige]

Originally Posted by I'm wrong

Oh I get better values than these...

So you drive <65 on the highways...