[scbim]

My car has been drinking gas like a fiend and I'm curious for input on likely culprits. Estimating roughly 14MPG city, 18 highway with an average of 16MPG. Recently reset the MPG module and haven't been driving hard so the numbers are a bit...disappointing.

First inclination is to replace the VANOS solenoids since they haven't been done (103k on the odometer). They're pricey little units so it would suck if they didn't make a difference. Hoping to get a little input before proceeding. Any thoughts?

[Brian86]

Malfunction codes please.

Nobody can help without knowing malfunction codes.

[TheMidnightNarwhal]

I mean I seem to average around 14L/100KM (~ 17 MPG). I thought that was normal unless you baby drive it strictly. I'd say around 12L 100/KM (19.6 MPG) on highway from what I recall. I wouldn't start shooting the parts cannon.

[scbim]

Okay I guess this is normal then? No error codes. Remember reading 19 city 24 highway somewhere but must have been mistaken...My buddy gets 19 with his V8 e39. Figured a ten years newer V6 might do better =/

[E93Dude]

I don't get people with healthy 335i's saying that sub 20mpg - even in city driving - is normal. Even driving like an absolute maniac asshole with my manual transmission, I have never seen poor mileage like that. I have healthy twin turbos that sit in moderate commuter traffic on a regular basis (15 miles each way, some stop-n-go, plenty of hills and traffic lights), and I average 25/26mpg without even thinking about it. I can get north of 28 if I pay attention to the throttle on green lights, and coasting. Best I ever got was 31 mpg cruising at a steady 72mph on flat highway.

I regularly use 93 octane, although when I have used 87, the mpg goes down. Years ago when my VANOS solenoids were gummed up, I took a rough idle/mpg hit, but again, never below 22mpg or so.

For those with persistent poor mpg, using proper octane is a given. Also, clean plugs, functioning coils and clean air filters are the easy first fixes. I would also suggest that if your car has over 100k miles, a walnut blast of the intakes is a MUST. Doing so helped my engine run smoother, and gave me an mpg boost.

[M-technik-3]

Winter fuel is diluted with crude which lowers the amount of power your car makes. I notice a drop of about 5 mpg come winter blend vs summer.

[scbim]

Originally Posted by E93Dude

I don't get people with healthy 335i's saying that sub 20mpg - even in city driving - is normal. Even driving like an absolute maniac asshole with my manual transmission, I have never seen poor mileage like that. I have healthy twin turbos that sit in moderate commuter traffic on a regular basis (15 miles each way, some stop-n-go, plenty of hills and traffic lights), and I average 25/26mpg without even thinking about it. I can get north of 28 if I pay attention to the throttle on green lights, and coasting. Best I ever got was 31 mpg cruising at a steady 72mph on flat highway.

I regularly use 93 octane, although when I have used 87, the mpg goes down. Years ago when my VANOS solenoids were gummed up, I took a rough idle/mpg hit, but again, never below 22mpg or so.

For those with persistent poor mpg, using proper octane is a given. Also, clean plugs, functioning coils and clean air filters are the easy first fixes. I would also suggest that if your car has over 100k miles, a walnut blast of the intakes is a MUST. Doing so helped my engine run smoother, and gave me an mpg boost.

Damn, 31? I'm getting close to 15mpg now, the more I drive around town the lower it goes and I rarely push above 4k rpm. Dirty valves and solenoids could be a factor. Plugs are fairly new. 91 is the highest octane I can buy out here but I use it religiously. Could give the solenoids a clean, although at 103k it seems like it might be worth just replacing them.

[scbim]

Originally Posted by M-technik-3

Winter fuel is diluted with crude which lowers the amount of power your car makes. I notice a drop of about 5 mpg come winter blend vs summer.

Interesting take, haven't heard of this before. Where are you located?

[M-technik-3]

It used to be reported higher but seems the feds don't want the masses complaining.

https://blog.amsoil.com/how-to-impro...r-gas-mileage/

https://afdc.energy.gov/files/pdfs/2876.pdf This study is for oxgenated fuel not or crap Ethanol and Ethanol attracts water which has no energy so I'm sticking to what I saw a few years back with 5%

[TheMidnightNarwhal]

Originally Posted by E93Dude

Best I ever got was 31 mpg cruising at a steady 72mph on flat highway.

I regularly use 93 octane, although when I have used 87, the mpg goes down. Years ago when my VANOS solenoids were gummed up, I took a rough idle/mpg hit, but again, never below 22mpg or so.

When you mention 31 mpg, are you referring to the instant read fuel economy or you reset your computer and then read the number it says after having only driven on the highway? My numbers are the average MPG is shows in the iDrive but if I do the instant read one, I can definitely hit 31 MPG as well cruising on a flat highway at 120km/h.

[TheMidnightNarwhal]

Originally Posted by scbim

Damn, 31? I'm getting close to 15mpg now, the more I drive around town the lower it goes and I rarely push above 4k rpm. Dirty valves and solenoids could be a factor. Plugs are fairly new. 91 is the highest octane I can buy out here but I use it religiously. Could give the solenoids a clean, although at 103k it seems like it might be worth just replacing them.

Oh in this case maybe something is wrong. I forgot to clarify my numbers were based on winter season here in Canada and I let it idle a bit not sure if it takes that in account for MPG. I'm also walnut blasted. Coils and plugs are still not changed idk when it was last time was done which I plan to do in summer.

[E93Dude]

Originally Posted by TheMidnightNarwhal

When you mention 31 mpg, are you referring to the instant read fuel economy or you reset your computer and then read the number it says after having only driven on the highway? My numbers are the average MPG is shows in the iDrive but if I do the instant read one, I can definitely hit 31 MPG as well cruising on a flat highway at 120km/h.

31 mpg averaged out over several tens of miles on cruise control for extended period - not instantaneous MPG. This was on a post walnut blast, plugs/coil refresh extended test drive. I mean, the originally advertised mpg was 30 highway anyway, so not surprising.

[TheMidnightNarwhal]

Originally Posted by E93Dude

31 mpg averaged out over several tens of miles on cruise control for extended period - not instantaneous MPG. This was on a post walnut blast, plugs/coil refresh extended test drive. I mean, the originally advertised mpg was 30 highway anyway, so not surprising.

I mean that is surprising tbh because advertised MPG is actually 20 combined, 17 city and 26 highway. Are you talking about the N54 or maybe N52 (328I)?

[E93Dude]

[QUOTE=TheMidnightNarwhal;29718235]I mean that is surprising tbh because advertised MPG is actually 20 combined, 17 city and 26 highway. Are you talking about the N54 or maybe N52 (328I)?

Hm….Im in a 2007 335i convertible with M/T. N54 twin turbos. I always thought the highway rating was 30, but I just checked fueleconomy.gov (managed by the EPA), and it says 17/26, 20 combined, so I stand corrected on the official stats. But those numbers bear no resemblance to what I am seeing, although part of that may be due to my having a dual cone intake, so free-er flowing air may make a difference. Maybe the motor being, shall we say…”well broken in” gives it overall reduced internal friction than a new per one? Interestingly, visitors to the site are able to self report individual mpg. One convertible 335i owner did, in fact, report 31.7 average mpg in largely highway driving.

[TheMidnightNarwhal]

[QUOTE=E93Dude;29718774]

Originally Posted by TheMidnightNarwhal

I mean that is surprising tbh because advertised MPG is actually 20 combined, 17 city and 26 highway. Are you talking about the N54 or maybe N52 (328I)?

Hm….Im in a 2007 335i convertible with M/T. N54 twin turbos. I always thought the highway rating was 30, but I just checked fueleconomy.gov (managed by the EPA), and it says 17/26, 20 combined, so I stand corrected on the official stats. But those numbers bear no resemblance to what I am seeing, although part of that may be due to my having a dual cone intake, so free-er flowing air may make a difference. Maybe the motor being, shall we say…”well broken in” gives it overall reduced internal friction than a new per one? Interestingly, visitors to the site are able to self report individual mpg. One convertible 335i owner did, in fact, report 31.7 average mpg in largely highway driving.

Interesting. But yeah maybe the MT is more fuel efficient.

For me it's 17 city, 24 highway and 19 combined. I guess I will do some testing myself this summer. I'm around 16mpg right now. But yeah I thought the consensus was that these ratings were actually difficult to reach lol. But I tend to floor it it's difficult to try just babying it to test lol.

[scbim]

Originally Posted by TheMidnightNarwhal

Oh in this case maybe something is wrong. I forgot to clarify my numbers were based on winter season here in Canada and I let it idle a bit not sure if it takes that in account for MPG. I'm also walnut blasted. Coils and plugs are still not changed idk when it was last time was done which I plan to do in summer.

Seems l like it could be doing better...Been babying the hell out of it mainly bc the mpg is so low. Don't like to drive hard til' it's warmed up either so it's pretty natural for me to keep the rpm's low around town. Not really sure where to start - best I can come up with is solenoid / valve clean. No leaks that I've noticed. HPFP was replaced around 50k

[johnnyorange]

just for fun (and im guessing here) but whenever i think anything could be problematic with vanos solenoids I always also take a look at the check valves

just a thought

fwiw in my lci e91 I always fill with 93 octane and have never been able to get my mpg readout to rise above 18.9mpg

i dont do a ton of highway and that is mostly city driving

its always bugged me that the mpg is not higher

[scbim]

Originally Posted by johnnyorange

just for fun (and im guessing here) but whenever i think anything could be problematic with vanos solenoids I always also take a look at the check valves

just a thought

fwiw in my lci e91 I always fill with 93 octane and have never been able to get my mpg readout to rise above 18.9mpg

i dont do a ton of highway and that is mostly city driving

its always bugged me that the mpg is not higher

Interesting, definitely mixed responses on that front. Might grab a borescope so I can check the valves, such a bitch getting that cover off though xD

[scbim]

Update: main issue identified as brake drag due to lack of grease on the caliper guide pins. After greasing those little buddies and resetting the fuel economy tracker I’m back up to 19mpg (with heavy footed driving, stop and go traffic, and a couple “Italian tune-ups”).