MPG dropped! anything i have missed???

[x5matt]

Hi Guys

05 3.0d auto........ mpg has dropped noticebly over the last few weeks, i know you get less litres for your £ but im sure there is something a miss with mine -

normally do motorway driving, have been averaging 32+ always. but over the last couple of weeks have noticed a drop and not sure why??

1. full service completed 3 months ago - inluding all filters (fuel) and Breather pipe. no smoke and no problems afterwards.
2. new fuel pump installed under warranty a few months ago and all has been good , no probs.

so not sure at all why the drop - now for the signs that i am para about -

1. new tyres fitted 500 miles ago - General grabber UHP's - but surley this would not affect the mpg to such a extreme??
2. engine sound a little noiser that before and i do feel a little vibration under my foot , but i put this down to the new tyres??
3. Maybe a exhaust issue?? its done 88k , would not expect it as yet??
4. turbo on the way out, it does feel a little sluggish???
5. injectors?? - it did give me rough idleing on standstilll but this was resolved once the new fuel pump was fitted and it doesnt do this anymore.

im a bit lost...... i reckon its dropped 15-20% in MPG.............. no smoke etc so i just dont know , its just more thirsty than before (much). Could it just actually be we are getting less at the pumps. I know my cars and beleive it is a issue, just trying to elimante the possibilites with MPG - never had to think about this problem before.

all input and suggestions would be great....... no matter how daft they may be as im lost.

thanks in advance

[fenj66]

Are you basing this on actual mpg calculations or are you just using the computer mpg info?

[x5matt]

Hi Fenj

no never really use the mpg computer as we all know it gives you differing figures dependant on town/motorway and time spent on motorway etc. so this is more that fact that you know how much you normally get from your car and you notice more if all of a sudden your filling up 3 times a week when you used to do twice a week and still doing the same miles.

when they fitted the tyres they had inflated them to 45psi all round, they were rock solid, i reduced them to the stanadard psi that i have used for years 33 rear 31 front which made for a more comfortable ride but now wondering if that may have done something? i was running Mich Diamars before.

also thinking MAF??

[fenj66]

Hmm, not sure then, other than double check air filter was actually changed! its a pig to get back bolts off.

[jaynana]

what are you talkin about - computer calculates mpg based on miles driven and fuel consumed. and u have 2 counters which can be reset at any time. nothing wrong or misleadin about that, that's pretty accurate i think.

range on the other hand can be misleading cos its based on mpg in the last so many miles and amt of fuel left. when mpg changes teh range changes (to say the obvious).

anyways, pointers for what can change mpg - driving style (even driver), city/motorway driving/traffic, fuel pump, injectors, tire pressure, accessories like roof racks which effect aerodynamics, weight of course, gear box (gears changing normally?), air filter...

[pvr]

He did not use computer ....

My swap to winter tyres dropped the mpg by 10% . Winter diesel reduces mpg as well, did you measure during the cold spell?

[dirtymonkey29]

New shoes with heavier soles

[fenj66]

The computer mpg figures can indeed be accurate, but also can be very easily manipulated to over or under read. If I so wished, I could make my computer show an average of 50 mpg!

[B5tew]

I have noticed similar I put it down to sat with the engine running every morning waiting for the windscreen to defrost in the cold weather
I have been having the car running for about 5 mins every morning and it then only takes me 10 mins to get to work so will probably make a big difference



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[ITBarbie]

Ive noticed a dip but then I did last year as well. It's always worse when it cold outside. I also had been using my auxiliary heater too so that's just as bad

[scooby1doo1]

So based on what your saying, your losing around 5 mpg.

Winter will lose you some mpg, in my 530d I lost 3-4 mpg.

In the X it's only a round 1-2 mpg, but this is a 3.0i so will warm up quicker in colder weather.

My bros lost a round the same in his 330d, add this to new tyres and maybe this adds up to your lose of miles.


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[x5matt]

Many thanks for all your replies. I am hoping it is just the tyres, do you feel my psi is correct 31 front 33/34 rear? . im am going to put a scanner on it later this week just to make sure its not showing any messages.

i do not normally use the computer, i normally go off the range, this is what i meant when i said it was not that reliable.

[ITBarbie]

Mine are 32 all round. Correct pressure setting on label on skin of drivers door

[x5matt]

thanks , i had a look at the sticker but i have always run around 31/33 all round. the thing is that 31/32 on the Mich Diamaris felt hard, on the new tyres (General Grabber UHP) 31, 32, and even 33 feel very underflated for some reason. Im not too happy with the tyres, the composite just feel a world away from the Mich's that i have always run. It was only cost that swayed me to these this time.

they even look underflated in comparison to the Mich's and i have checked 3 different petrol station to make sure they do have 31 front, 33 rear, may try 32's all round and see how they feel.

i think they may have much softer sidewalls, but was expecting the opposite from a lower brand of tyre than the Mich's............oh well will keep fine tuning!!!!