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Discussion Starter #1
Not sure if this is outside of my control, but recently (weeks maybe months) my i-shift's mpg is taken a nosedive. I commute 250 miles a week and have noticed that I'm using more fuel each week with a similar driving style. It's down about 5+ mpg on a 1.8 i-shift

Things I've checked...
  • Driving style, keeping to 63mph on the M'way does help but the mpg does seem to be down
  • Decluttered the boot
  • Tyre pressure (all at 32 for R17 tyres)

Things that I've noticed
  • It's cold. Duh! Would that make a huge difference?
  • It's a petrol i-shift. It does rev quite high and holds onto gears longer (might this be due to the cold)

Things that have changed recently
  • Someone (not me) kerbed a wheel badly recently and (long story short) I've now got 3x Bridgestone S01 tyres which are quite frankly horrible. They have a high rolling resistance (according to reviews) :-( but they have been on for a few months and the nosedive has occurred recently (I think, these things creep up?)
  • The i-shift had it's upgrade to new software as part of it's yearly service/recall in the summer
  • The dealer used a "engine cleaner" to improve mpg as part of the service in the summer

Thinking about the i-shift, I would always put the car into neutral when stopped, how can you tell if an i-shift clutch is slipping? Is poor mpg a symptom along with occasional high revving?

If it's nothing mechanical then I'm just looking at poor weather, tyres and driving style; things under my control :VTECSMILEY:

Any advice on what to check?
 

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Geek :)
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My derv was down to 39.2 mpg for the last 110 miles. I only do 9 miles each way a day but I'd say it's down to the cold.
 

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Supporter
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winter fuel and the added items such as aircon, heated widows etc all take their toll, there is a thread about somewhere
 

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Premium Member
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Cold weather causes that kind of loss of mpg. The car takes longer to warm up and so runs richer for longer. Also the air is more dense so the car injects more fuel and you have more power in winter.
 

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My diesel is well down, shorter thanusual journeys and cold weather to blame.
 

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My 1.8 I-Shift petrol is down from around 38/39 to 33/34 driving style hasn't changed. Updated software last week, but I'm sure it's down to drop in temperature. My FTO loved this time of year.
 

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Not sure if this is outside of my control, but recently (weeks maybe months) my i-shift's mpg is taken a nosedive. I commute 250 miles a week and have noticed that I'm using more fuel each week with a similar driving style. It's down about 5+ mpg on a 1.8 i-shift

Things I've checked...
  • Driving style, keeping to 63mph on the M'way does help but the mpg does seem to be down
  • Decluttered the boot
  • Tyre pressure (all at 32 for R17 tyres)

Things that I've noticed
  • It's cold. Duh! Would that make a huge difference?
  • It's a petrol i-shift. It does rev quite high and holds onto gears longer (might this be due to the cold)

Things that have changed recently
  • Someone (not me) kerbed a wheel badly recently and (long story short) I've now got 3x Bridgestone S01 tyres which are quite frankly horrible. They have a high rolling resistance (according to reviews) :-( but they have been on for a few months and the nosedive has occurred recently (I think, these things creep up?)
  • The i-shift had it's upgrade to new software as part of it's yearly service/recall in the summer
  • The dealer used a "engine cleaner" to improve mpg as part of the service in the summer

Thinking about the i-shift, I would always put the car into neutral when stopped, how can you tell if an i-shift clutch is slipping? Is poor mpg a symptom along with occasional high revving?

If it's nothing mechanical then I'm just looking at poor weather, tyres and driving style; things under my control :VTECSMILEY:

Any advice on what to check?
It's winter - its a normal drop.

What do you have the heater set to?

- Personally, I'd run the pressures a bit higher than that - I'm at 35-36psi.
- Don't have the heater on high for the first couple of miles.
- Minimise seat heaters/rear window heater etc
- Clear car of snow
- Don't warm the car up on the drive
 

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Keep On Vtec'ing!
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553 Posts
Cold weather causes that kind of loss of mpg. The car takes longer to warm up and so runs richer for longer. Also the air is more dense so the car injects more fuel and you have more power in winter.
my CTR's MPG seems to have dived to just about 20mpg (according to trip computer) and ive been driving extremly sensibly in this cold weather.

Damn you cold weather!!
 

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Premium Member
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my CTR's MPG seems to have dived to just about 20mpg (according to trip computer) and ive been driving extremly sensibly in this cold weather.

Damn you cold weather!!
Wow! Makes my dive to 43 mpg look like nothing!
 

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i would expect 5% decrease on mpg due to cold weather. but on long journeys, running rich on startup doesn't add to much to the average values...any thoughts about spark plugs?
 

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i would expect 5% decrease on mpg due to cold weather. but on long journeys, running rich on startup doesn't add to much to the average values...any thoughts about spark plugs?
Cold air is denser so the car will inject more fuel and make more power. Whilst not running rich at this stage it is still injecting more fuel than it would in the summer. Spark plugs are a service item so replaced after a set period.
 

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Premium Member
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i would expect 5% decrease on mpg due to cold weather. but on long journeys, running rich on startup doesn't add to much to the average values..
My thoughts and findings too. If doing ~20 journeys then I've found the cold weather makes little difference to my economy. In fact on some cold foggy days my mpg improved as I was driving slower.

To the OP: Are the roads busier than normal? Maybe you're having to decelerate and accelerate more than before.
 

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aka Paul
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If your wheel has had a knock I'd be getting the tracking checked. Are you getting any uneven wear on any of the tyres?
 

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I do not run my A/C during winter.

Just turn it to Hi and let the fan run by itself but then again it does not snow here.

Cold air is denser so the car will inject more fuel and make more power. Whilst not running rich at this stage it is still injecting more fuel than it would in the summer. Spark plugs are a service item so replaced after a set period.
Also being denser it is more thicker to move through so you have more resistance.
 

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i have an i shift and havent seen mine above 30 for a good few months

Out of interest what's your average speed on the trip comp?

Recently discussed on a similar thread, often linked to the average speed even if the commute stays same, the weather + traffic doesn't

p.s

My iShift gets 25-27mpg at an average of 11-13mph
 

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Premium Member
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Out of interest what's your average speed on the trip comp?

Recently discussed on a similar thread, often linked to the average speed even if the commute stays same, the weather + traffic doesn't

p.s

My iShift gets 25-27mpg at an average of 11-13mph
last i noticed was 17mph but ill check tonight let you know
 

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Premium Member
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29 Posts
Discussion Starter #20
Cheers guys...

I'll up the pressures a bit on the tyres. Though the ride quality on them is pretty poor (going back to P6000s after this I think) [smilie=puking.gif]

As for tracking I'm due an MOT in a couple of weeks, going to the local Formula 1 autocentre. I'll get them to doublecheck the tracking after the MOT.

The tyre that replaced the one that got knocked "looks okay". I saw it up close and personal quite a bit whilst changing the foglamp.

Chris
 
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