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Discussion Starter · #1 ·
Hey guys,

In the last few weeks i've noticed that my car has been using my petrol than normal. I would normally get approx. 400kms from full until the light comes on. My driving style or the amount of traffic i'm getting stuck in hasn't really changed but I seem to be getting about 50kms less per tank.
I've also noticed that the car is idling higher than normal once started in the morning. It seems to be idling about 2k, and even though the weather has got a lot colder, it doesn't really effect me as my car is parked in an underground carpark which isn't anywhere close to being as cold as it is outside. The car also seems be a bit lumpy for the first couple of minutes of driving.
I had the car dyno'd about 5 or 6 weeks ago, and they said it was running a small bit rich, however at the time I was still getting 400kms from the tank.
Anybody any ideas on what could be causing this?
 

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Not sure about denser air...but factors can be...

Cooler engine for longer = Richer fuel mixture for longer = more consumption
Tyre pressures drop in cooler air, resulting in more rolling resistance - best check and top up.
Cooler engine for longer = Drag in lubricants in the engine = engine works harder
More electrical loading - Window/mirror heaters, more lights, more cabin heater, more washer pump


Pump yer tyres up, don't idle the car to warm it up, scrape the frost of the windows and don't use the window heater, wrap up warm and leave the heater off :)
 

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Discussion Starter · #6 ·
Thanks for the replies so far guys.


I should have noted that when I said the cars is idling higher than normal when it's started up in the morning, I know it idles higher first thing in the morning to help warm up, I meant that it is idling even higher than it normally is.
And the same applies to the car being lumpy too, it just feels more lumpy than it normally does.
As I also said in my previous post, bare in mind that I park in an underground carpark that isn't cold, so it's not the winter weather effecting the initial start and high idling.


Not sure about denser air...but factors can be...

Cooler engine for longer = Richer fuel mixture for longer = more consumption
Tyre pressures drop in cooler air, resulting in more rolling resistance - best check and top up.
Cooler engine for longer = Drag in lubricants in the engine = engine works harder
More electrical loading - Window/mirror heaters, more lights, more cabin heater, more washer pump


Pump yer tyres up, don't idle the car to warm it up, scrape the frost of the windows and don't use the window heater, wrap up warm and leave the heater off :)
Using electronics has literally no difference to fuel consumption. And even if it did, it would make no difference in this case, as virtually everytime I drive the air con is on.

While the above points may make a very small difference on the MPG, they aren't the case here. There is no way the above reasons would equal to about a 60km difference per tank. 340km instead of 400km is a big difference.
In 10 years of driving, i've also never had a noticeable difference in MPG during the winter months.

I was thinking that it is possibly down tot he O2 sensors needing to be changed/cleaned which is causing the car to run too rich?
 

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idling at 2k sounds a bit high , mines a 1.8 and it idles 1.5k max at cold start.
 

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My opinion has always been that the fuel tank, being long, wide, thin and underfloor suffers from cold weather more so than a conventional tank that is more shielded.
 

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Thanks for the replies so far guys.


I should have noted that when I said the cars is idling higher than normal when it's started up in the morning, I know it idles higher first thing in the morning to help warm up, I meant that it is idling even higher than it normally is.
And the same applies to the car being lumpy too, it just feels more lumpy than it normally does.
As I also said in my previous post, bare in mind that I park in an underground carpark that isn't cold, so it's not the winter weather effecting the initial start and high idling.




Using electronics has literally no difference to fuel consumption. And even if it did, it would make no difference in this case, as virtually everytime I drive the air con is on.

While the above points may make a very small difference on the MPG, they aren't the case here. There is no way the above reasons would equal to about a 60km difference per tank. 340km instead of 400km is a big difference.
In 10 years of driving, i've also never had a noticeable difference in MPG during the winter months.

I was thinking that it is possibly down tot he O2 sensors needing to be changed/cleaned which is causing the car to run too rich?
The power that drives all that kit comes from the alternator that is driven by your engine which uses fuel. If it didn't make any difference, BMW, Toyota wouldn't be spending R&D on fancy alternators that generate the electricity more efficiently.

It isn't the only thing that results in increased consumption in winter, but it will contribute.

Sent from my GT-I9000 using Tapatalk
 

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Discussion Starter · #16 ·
All FN2s should be running at 2000 rpm when cold this is nornal,once warm it will drop to 750-800 rpm.
Mine has never idled at 2k before now, it's always been closer to 1.5k :confused:

BDJW when was the last time your car was serviced?
4.5k kms ago. It was also on a dyno a few weeks back, a dyno which is considered to be very tough on cars and it made just over 200bhp, so it is running quite well. As I said above, they thought it was running slightly rich though.

The power that drives all that kit comes from the alternator that is driven by your engine which uses fuel. If it didn't make any difference, BMW, Toyota wouldn't be spending R&D on fancy alternators that generate the electricity more efficiently.

It isn't the only thing that results in increased consumption in winter, but it will contribute.

Sent from my GT-I9000 using Tapatalk
In my experience it makes very little difference. And as I already stated, in this case it has no bearing on the difference in fuel consumption because no matter what time of the year it is, I always have the same electronics on!
 
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