Drop in MPG

[kieranjholland]

I've been achieving 28-30 mpg in my BMW E61 525i (efficient dynamics/LCI) and have been relatively happy with this return based on my driving.

At the beginning of this week 2 things happened:
1. The weather went from 8C/10C to -3/0C
2. My mpg dropped from 28/30mpg to 22/24mpg

I should add, nothing has changed in my driving habits other than I let the car warm up for 5 mins longer before leaving.

I've never experienced such a large drop in mpg simply due to weather so am a little confused. I take it this isn't normal?

NB BMWs have a little real time mpg gage in the dash which used to correlate directly with the avg. counter when it is reset however since the beginning of this week the avg. counter is now showing a lot less (5-10mpg) that the real time gage. Therefore, I'm led to believe there may be more of an issue…

Edited by kieranjholland on Tuesday 17th January 22:10

[V88Dicky]

It's perfectly normal I'm afraid. My 2.0 petrol has dropped from 45 to 41mpg during this cold spell.

[DanielC4GP]

Yeah perfectly normal mines droppped from 31mpg to 28.5.

[Dave_newcastle]

And my 2002 E39 525i from 30.3 MPG to 28.2 MPG

[TaffRichie]

Sadly the ECU puts in more fuel in cold weather, mainly when the engine is getting upto full operating temperature.

[siwil1]

so you leave the car idling for 5 mins and expect consumption to remain the same

I bet you have had fans/ aircon on full and heated rear window aswell but obv none of these would effect mpg.

[kieranjholland]

TaffRichie said:

Sadly the ECU puts in more fuel in cold weather, mainly when the engine is getting upto full operating temperature.

Great... more fuel for my house to get warm and more fuel for my engine to get warm!

Dave_newcastle said:

And my 2002 E39 525i from 30.3 MPG to 28.2 MPG

Does your real time mpg gage match your average (when reset you can usually see them match quite closely normally) as mine is now way out. Interestingly the same amount out as the drop in my average mpg (around 7 mpg). Confused.

siwil1 said:

so you leave the car idling for 5 mins and expect consumption to remain the same

No, I thought I was clear: 5 minutes longer than normal, maybe even 10.

siwil1 said:

I bet you have had fans/ aircon on full and heated rear window aswell but obv none of these would effect mpg.

How much do you want to bet

Thank you for your input...

Edited by kieranjholland on Tuesday 17th January 22:33

[vit4]

39 mpg to 34 mpg

[cahami]

double check tyre pressures

[icepop]

Yeah, know what you mean, my diesel has dropped from around 60 to 59, bummer, eh!!!!!

[kieranjholland]

icepop said:

Yeah, know what you mean, my diesel has dropped from around 60 to 59, bummer, eh!!!!!

Flip you!! I've just moved from diesel, I used to achieve 58-60 too

Edited by kieranjholland on Tuesday 17th January 22:36

[chris182]

Yep, 40 in the summer to 38 in the cold.

[icepop]

Not really pal, only joshing, my 2lt VAG diesel has dropped from a hardly impressive 46 to a demoralising 41mpg. The 1.8t petrol VAG does 38 on a run. Mmmhhh, I sense a change of propellent coming on at the next vehicle swap.

[halo34]

Dropped from 47 ish down to 39!!

Diesel though and its been absolutely baltic here - got back up to 42 by staying in a lower gear when cruising to keep engine temp up on the flat.

Ok I was perhaps using my right foot more than normal recently.....maybe allot more

[kieranjholland]

vit4 said:

39 mpg to 34 mpg

Yep, it's pretty poo.

It's also a little concerning which is why I posted as I won't stick on every device in the car whilst warming it or drivng it due to the impact on mpg... as siwil1 pointed out so eloquently above

[Fox-]

Not really noticed a drop here.

[Jimmyarm]

Odd how cooler temps are better for performance but not mpg

BMW engines have had electronic thermostats in them for some to allow the engine to run hotter when cruising for increased mpg.

[ensignia]

Gone from 20mpg to 16mpg recently

[sebhaque]

My M3 has been returning 23.3 mpg according to the trip computer thing. Considering that's mostly motorway running, I think I've dropped some mpg - although I don't really bother with mpg much any more, it's not exactly the kind of car that you drive in an economical matter!

[EDLT]

kieranjholland said:

siwil1 said:

so you leave the car idling for 5 mins and expect consumption to remain the same

No, I thought I was clear: 5 minutes longer than normal, maybe even 10.