Erratic MPG - Page 2 - Fuelly Forums

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Old 01-04-2013, 09:32 PM   #11
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Well there are lots of factors involved, the main one is probably the type of daily journey you do. I am fortunate in that I have only a small amount of urban driving, and that is with few stops, and a long enough motorway drive to warm up the engine properly.

Other factors are:

* Top motorway cruising speed, since aerodynamic drag is the greatest consumer of fuel when you are motorway driving

* Aerodynamics, the A2 has a CD of 0.28 - 0.25 depending on model. I also installed aero components to try to improve this.

* Weight (the A2 has an aluminium chassis not steel)

* Tyre pressure (must always be >= recommendation, never below)

* LRR tyres

* Current temperature (at the moment my mpg has dropped dramatically thanks to winter)

* Windspeed & direction - driving into even a gentle headwind on the motorway will reduce your mpg

* No short journeys!!! Your fuel efficiency is only good once the engine has fully warmed up.

* RPM. I spent £1400 on a gearbox upgrade in order to reduce my RPMs on the motorway. I also drop the car into neutral on gentle downhills etc (but keep it in gear if you need to slow down or it is a steep hill).

Have a good weekend yourself :-)
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Old 01-05-2013, 12:05 AM   #12
gpk
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Yes I see from the official stats that the A2 has better cruising consumption than the Polo and yr 6th gear presumably makes it even better. Am not entirely convinced by the neutral thing though because that might cause more fuel to be used keeping the engine ticking over, rather than letting the car's momentum achieve this?
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Old 01-05-2013, 02:29 AM   #13
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>Am not entirely convinced by the neutral thing though because that might cause more

>fuel to be used keeping the engine ticking over, rather than letting the car's

>momentum achieve this?

While it's true that neutral uses some fuel to keep spinning, whereas in-gear uses no fuel, the problem is that when you are in-gear you are engine-braking and hence slow down quicker (due to the friction etc of keeping the engine spinning at high revs). So the total energy loss is greater in-gear than in neutral. Hence if you want to slow down (engine-brake), in-gear is best. But if you want to keep moving, then neutral is best.

Take a look at page 3 of the following link:

http://thinkblue.volkswagen.com/en_US/fuel_saving_tips
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Old 01-05-2013, 05:16 AM   #14
gpk
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I guess it depends a bit what gear you are in :-)

Looks like tickover is very economical these days. From following another link. Did always strike me as a bit weird, those people who coasted with clutch in or in neutral....! But maybe their time has come!
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Old 01-05-2013, 05:41 PM   #15
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>...Looks like tickover is very economical these days...

Because diesel engines run lean, they have always been economical in tickover. However petrol cars have to run a richer mixture & hence waste a lot more fuel when idling.
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Old 01-05-2013, 08:58 PM   #16
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OK now I'm lost...!!! Will go and read up on the subject. One day. Maybe! ;-)
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Old 02-02-2013, 04:06 AM   #17
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I have the same issue... wildly erratic graphing.

Does Fuelly have a way to give a rolling 3 or4 tank average overlaid on the mileage graph so that the user can track the trend rather than just see the raw data points?

Thanks in advance.

Hugh
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Old 02-03-2013, 04:13 AM   #18
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Doesn't seem to be that erratic... ? Within a band of a few MPG which is as close as is practical.
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