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[platty]

Hi Guys,

Don't know if anyone else has noticed any sort of drop in economy during this cold spell, but I seem to have lost quite a few miles per tank based upon the same sort of driving. Rather than getting 550 from a tank, I am barely seeing 450 an equivalent drop of about 6mpg.

I am assuming this is mainly down to the car being on choke for longer when started from cold - any other factors?

Anyone else notice such a difference?

[Abiton]

Mainly due to extended warm-up, but also possibly slightly affected by the air that you're driving through being denser, and so harder to push out of the way.

Wouldn't like to try and quantify the latter.

[tunnie]

heated seats, heated screen, heaters, all take a hit on the mpg, mines dropped by about 5-6 mpg

[tigers_gonads]

i'll agree too all that 
waiting for the car to defrost and the oil to warm through / lots of stop / start in the snow 
only getting about 25mpg at the moment 

[mathewst]

Every single electronic powered device will cause a drop in mpg.
Driving with aircon on will cause an increase of 1 or even 2 litres per 100 km.
Driving with heating (eco) will also increase consumption but not so much.
Even lights cause an increase of 0.2 to 0.5 litres by some estimates.
Also the car takes longer to warm up, and usually speed is worse in the cold, wet cause of more breaking, acceleration etc.

[Bionic]

As they have already said, if the motor is working harder by having to take longer to warm up, generate more power for all the extra electrical gadgets in use, use more fuel by ticking over in traffic queues etc all have an impact on mpg. Nothing is ever cut and dried and the so called 'average' figures that are repeadly quoted have no validity. We all drive totally differently and even if we all drove the same car over the same distance and route the mpg would be radically different between us all. Fact of life I am afraid.
I currently get around 21 in town and 39 on a run. Usually it is 25/27and 43/48.

[feeutfo]

there was an intresting thread in the gallery by cateramv6 a couple of weeks back re warm air induction, he basicly fitted a cone filter directly over the exhaust manifold, warmer air means bigger air molecules, which means less air molecules can get in to the engine which means less fuel injected to match the air flow. Means less power but who cares when you just want to get out of your drive to work...

basicly cold air means more fuel and more power. Ever noticed an engine run better in cold air? certainly notice it on a bike.

[Abiton]

Yeah, but the MAF has temperature compensation for just this reason doesn't it?
Should keep the fuelling in proportion to the mass of air going in, irrespective of density???

[feeutfo]

Yeah, but the MAF has temperature compensation for just this reason doesn't it?
Should keep the fuelling in proportion to the mass of air going in, irrespective of density???

all in here
http://www.omegaowners.com/forum/YaBB.pl?num=1261325703

[Kevin Wood]

Yeah, but the MAF has temperature compensation for just this reason doesn't it?
Should keep the fuelling in proportion to the mass of air going in, irrespective of density???

Yes, it does. However, if you're not actually using the full power it is very slightly more efficient to have less dense air and open the throttle a bit wider to compensate. I'm not convinced it makes enough difference to be worth bothering, which is borne out by the fact that the car doesn't have its' own hot/cold air valve driven by the ECU.

Kevin

[Abiton]

Aha, I didn't think about reduced pumping losses.   

I certainly need warm (well 20°C) air for my Golf to work well, as it has one of those quaint carburettor things. 
VW use a vacuum motor to move a flap on most of their older engines.

[feeutfo]

Aha, I didn't think about reduced pumping losses.   

I certainly need warm (well 20°C) air for my Golf to work well, as it has one of those quaint carburettor things. 
VW use a vacuum motor to move a flap on most of their older engines.

yours may have a warm air flap then, my Mrs polo has one as said in that thread.
 

[feeutfo]

Aha, I didn't think about reduced pumping losses.   

I certainly need warm (well 20°C) air for my Golf to work well, as it has one of those quaint carburettor things. 
VW use a vacuum motor to move a flap on most of their older engines.

yours may have a warm air flap then, my Mrs polo has one as said in that thread.
 

although maybr not if its carb?

[Abiton]

Yep, airbox has a (bimetallic) thermostat that controls the vac motor, which moves the flap between cold and warm air feeds to try to maintain 20C.  More or less essential with carbs, and used instead of coolant heating of the TB on injected dubs (dunno about recent ones). Your missus's will be the same, I'd say.   

[Rockhampton]

there was an intresting thread in the gallery by cateramv6 a couple of weeks back re warm air induction, he basicly fitted a cone filter directly over the exhaust manifold, warmer air means bigger air molecules, which means less air molecules can get in to the engine which means less fuel injected to match the air flow. Means less power but who cares when you just want to get out of your drive to work...

basicly cold air means more fuel and more power. Ever noticed an engine run better in cold air? certainly notice it on a bike.

I have to agree - my Saab 900 Turbo was always much better in the cold - much nicer power delivery