mornin` all

just come in to work, normal 35 mile motorway run... but today its cold (12 deg on the computer)..... usual average for the run is 53-55 mpg.... thats average over the last few week in fairly warm weather (15 deg to 25 deg)

today i struggled to get 44mpg.... I also noticed the same this last weekend, driving early on Sunday morning, sunny but cold again, 12 deg and same thing, mid 40's mpg for the motorway....

anyone else have MPG affected by the temperature this much? is this normal for diesels? if there any thing I can check on mine/ask the dealer to do??

cheers

Well I rarely ever get much more than about 46 even on motorways, so I wouldnt worry about it.

surely you'd expect better mpg on cold days cos the cold air gives more 'bang for yer buck' and less diesel would be needed for the same performance?- just a thought. :confused:

yeah totally agree with that comment, thats the theory I was going for.... i.e. colder air = more dense = more O2 for the burn.... BUT i had a similar thing with my old VR6...

on cold days (outside air temp) even when both water and oil temps were up to normal it would get slightly lower MPG, but never quite this bad, more like 1 - 2 mpg less at 30mpg average

and as for rarely getting more than 46mpg on the motorway, i guess that depends how fast you go

surely you'd expect better mpg on cold days cos the cold air gives more 'bang for yer buck' and less diesel would be needed for the same performance?- just a thought. :confused:

Surely it's the fuel/air mix that gives more bang for the buck? So the more air you can get in (cos it's cold and dense) the more fuel you can mix with it, hence more power. I also think running the heaters, etc may be a factor in the winter, but I'm not sure how significant that is...........

Chris

i had no heater on, no air con, just the radio!

more air = more fuel = more power = less throttle required = similar mpg, surely

Diesel combustion works by the increase in temperature and pressure by compressing the air...so if the compressed air is warmer, it will combust better. Warm air is less dense though, so you don't get as much expansion as you do with cold air.

So the ideal situation is warm cylinders but a cold air charge...however, diesel engines take a lot longer to warm up, hence you'll get relative innefficieny for longer (especially while the cold oil is warming up).

Once up to speed, you should see better instantaneous MPG, but your average will probably be down...

Rob.

i was watching the instantaneous MPG, and that was definately down on normal... will keep an eye on it, see what happens this evening, but i expect it to be warmer by 5pm

What a difference between TDi's the vRS sruggles to get 45 and the TDi get's this

yeah but we go faster

i had no heater on, no air con, just the radio!

well thats your answer turn the radio off...........must be taking up too much power! :P ok I'll get back in my box now

You think thats bad !!!!

I struggle to get 40 MPG sometimes, this morning going into work (10 miles) average was 46 MPG and that was in serious Granny mode.

I've just done the reverse journey again in Granny mode not exceeding 40 MPH and got 49 MPG.

I've done 2200 miles now and the overall average is 36 MPG :eek: , how on earth do some people get 60-70 MPG from a vRS.

Also remember to take into account the humidity of the air. Colder air could have more water vapour in it than warmer air, this could conceivably lead to lower MPG. ie not as much O2 more H2O.

You think thats bad !!!!

I struggle to get 40 MPG sometimes' date=' this morning going into work (10 miles) average was 46 MPG and that was in serious Granny mode.

I've just done the reverse journey again in Granny mode not exceeding 40 MPH and got 49 MPG.

I've done 2200 miles now and the overall average is 36 MPG :eek: , how on earth do some people get 60-70 MPG from a vRS.[/quote']

easy dont drive quick and keep the engine just about 2k but below 2.5 also it does get better with age so I've been told ...........the car that is.

Also you need to change your driving style if coming from a petrol. Learning which gears to use and when helps to.

ouch! but my mileage is on motorways... average at the pump is 51mpg (computer over reads by 3mpg)..... 1500 miles only so far, so still some running in to do

usual (warm day) cruising at 75-80 I get 53mpg average.... but anyway its still a great car and looks a tad nicer than a TDI!!

easy dont drive quick and keep the engine just about 2k but below 2.5 also it does get better with age so I've been told ...........the car that is.

Also you need to change your driving style if coming from a petrol. Learning which gears to use and when helps to.

I'd say after 10k miles I was pretty used to it and drive pretty much like you say, but like Buzz L I always struggle to get what some people on here claim to get.

I have a few theories. The people who get higher tend to live in places with less hills, and commute in places with less congestion. I have steep banks and congestion to deal with on a daily basis, and so what I get is not really disappointing to me.

Anyway, Buzz, welcome to team "less than 45 MPG out of a vRS"

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I have a few theories. The people who get higher tend to live in places with less hills' date=' and commute in places with less congestion. I have steep banks and congestion to deal with on a daily basis, and so what I get is not really disappointing to me.

[/quote']

I live in a hilly area and in a major city, doesn't stop you getting good milage but there is a knack to it and it takes time. You have to drive a diesel differently, and milage always helps the diesels fuel economy. I hardly use 1st and 3rd gears in town. 1st gets me rolling to about 5 mph, use second up to 25mph then 3rd to 30-ish before leaving it in 4th. If you are going through a 30 area you can put it in 5th and sit with all feet off the pedals as tickover in 5th is exactly 30mph although I don't!

I hardly use 1st and 3rd gears in town.

Are you saying you pull away in second? Surely thats not good for the clutch?

1st gets me rolling to about 5 mph, use second up to 25mph then 3rd to 30-ish before leaving it in 4th.

Leaving it in 4th at 30 quite often means you need more pressure on the accelerator to maintain speed. I've tried 3rd and 4th using the instant MPG reading and it can often be better in 3rd when the engine is not labouring.

If you are going through a 30 area you can put it in 5th and sit with all feet off the pedals as tickover in 5th is exactly 30mph although I don't!

I'm sure I read somewhere thats not good for it either.

I've found high gear low revs do not equal good fuel consumption. Hence what I meant by learning the gears. Every gear has what I call it's G-Spot where is gives the best fuel consumption.

Being stuck in traffic does make a difference but hills do not as such, dont forget what goes up has to come down, yes you may use more fuel going up but you save fuel coming down. Also planning ahead helps your fuel consumption.

I've tried 3rd and 4th using the instant MPG reading and it can often be better in 3rd when the engine is not labouring.

Colin has a 5-speed so it may well be different. I tend to agree with his findings though, although I have noticed that if you drive at 30mph in 5th, and the revs

drop below 1k rpm, the car has some kind of anti-stall mechanism which sharply accelerates the car until it's above 1k rpm. Bit of a shock the first time that happened! :eek:

Chris

Are you saying you pull away in second? Surely thats not good for the clutch?

No don't pull away in second, just use first to get it rolling before putting it into second at about 5mph and using the torque form 1300rpm to This seems fine for the car and it is not laboured in any way otherwise I wouldn't get good acceleration! 1st is a gear for getting rolling only from stationary, but too many people like my mates use it far too long. I also won't stop at roundabouts. I will keep it in second and keep rolling, not actually stopping. HGV and bus drivers will know this technique too.

Leaving it in 4th at 30 quite often means you need more pressure on the accelerator to maintain speed. I've tried 3rd and 4th using the instant MPG reading and it can often be better in 3rd when the engine is not labouring.

I fine the engine is fine in 4th at speedo 35mph. Remember that my engine is different, and gear ratios might vary too. I get the best results in 4th gear than 3rd and I've tried both on my drive. Not much difference but 4th does use slightly less fuel. For speedo 35mph I use 4th everywhere and get decent results- 4th is 60mpg on instantanous, 3rd is 45mpg. Acceleration is o.k too suggesting that it is not labouring. It is definatly not labouring however, that would be serious and I would never do that to a car. Problem I have with 3rd is that it has more engine braking than 4th, 4th you only need to feather it with small presses every 5 seconds or so to keep it on 35.

Oh and I never drive at tick over just using the torque to keep it going, as it is not good! I did it to prove a point to my petrol driving mates!

My drive home yesterday was done in 18 mins, over 6 miles, at an average speed of 22mph and a 78mpg average. That was particularly good hence how I noticed! This is despite it being rush hour and having to cope with ring road traffic and I find at 35 you get amostas good a mpg as as 55 on the motorway. Most of the time however it's mid 50's. Modern engines are really good at using no fuel if you are rolling in gear, second is very good for that, however as you say you should beware clutch damage if you pull away in second, which I only evr do in snow.