Author Topic: 29 mpg in 100% urban environment. Is this normal or what should I check?  (Read 1616 times)

TG

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Re: 29 mpg in 100% urban environment. Is this normal or what should I check?
« Reply #30 on: January 11, 2018, 03:32:58 PM »
Does anyone know if the Audi is fitted with the very expensive 'particulate filter?' which I believe loves this sort of treatment.
At the risk of increasing your blood pressure any further, probably this one has been removed and had a 12mm drill bit put through several times as an 'improvement'.
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TG

TG

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Re: 29 mpg in 100% urban environment. Is this normal or what should I check?
« Reply #31 on: January 11, 2018, 04:11:46 PM »
With the Jazz weighing 1100 Kg saving weight of half a tank of fuel (less than 20kg) is hardly going to make any measurable difference.....
I think I demonstrated the maths for this a while ago, at low speed it does not matter but at higher speed the energy required to accelerate a mass is definitely a reason to save weight.

It takes 14x more energy to accelerate a mass from 65 to 75mph than from 0 to 10 mph.  The extra 20kg subjected to a varying speed wastes energy.  It takes ~200 Joules to lift 20 kg by 1 meter, it takes ~3000 J to accelerate that mass from 65 to 75 mph.  This has nothing to do with drag, these figures would be the same in a vacuum.  Carrying the unused half of your tank around is like lifting a 20kg bag of sand into your boot 15 times every time your speed increases 10mph on the motorway.  Of course this is where cruise control wins.
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TG

culzean

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Re: 29 mpg in 100% urban environment. Is this normal or what should I check?
« Reply #32 on: January 11, 2018, 04:43:34 PM »
With the Jazz weighing 1100 Kg saving weight of half a tank of fuel (less than 20kg) is hardly going to make any measurable difference.....
I think I demonstrated the maths for this a while ago, at low speed it does not matter but at higher speed the energy required to accelerate a mass is definitely a reason to save weight.

It takes 14x more energy to accelerate a mass from 65 to 75mph than from 0 to 10 mph.  The extra 20kg subjected to a varying speed wastes energy.  It takes ~200 Joules to lift 20 kg by 1 meter, it takes ~3000 J to accelerate that mass from 65 to 75 mph.  This has nothing to do with drag, these figures would be the same in a vacuum.  Carrying the unused half of your tank around is like lifting a 20kg bag of sand into your boot 15 times every time your speed increases 10mph on the motorway.  Of course this is where cruise control wins.
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TG

The OP did say that he only does very short Urban (presumably low speed journeys if he wants to keep his licence).

Most people (including RAC and Honest John) agree that cruise control is OK on the flat but on both up and down gradients can make fuel consumption worse.
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

applicationcen

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Re: 29 mpg in 100% urban environment. Is this normal or what should I check?
« Reply #33 on: January 11, 2018, 05:18:45 PM »

From a semi-auto iShift point of view 29 mpg is a bit low even in demanding urban.

From a CVT point of view people recognise CVTs do not quite hit the same efficiency as a manual.

29 is very much in the broad range one might expect so it is unlikely there is anything wrong with the car, assuming you are topping up your lubes & fluids at service times.


eagle123

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Re: 29 mpg in 100% urban environment. Is this normal or what should I check?
« Reply #34 on: January 11, 2018, 07:31:23 PM »

From a semi-auto iShift point of view 29 mpg is a bit low even in demanding urban.

From a CVT point of view people recognise CVTs do not quite hit the same efficiency as a manual.

29 is very much in the broad range one might expect so it is unlikely there is anything wrong with the car, assuming you are topping up your lubes & fluids at service times.
True it is low wondering if the fuel consumption has improved compared to cars of the 90s as doing short journeys my mark one jazz was averaging like 32 mpg in winter these were short start stop journeys.
I had a 1.4 petrol astra 1994 with a high torque engine the fuel consumption was similar.

Driving style maintaining the car using genuine parts the correct oils does affect fuel econmy.

The most I had on my mk 1 jazz was 47 mpg on the motorway and that was 40 mph and in 5th gear.

I wanted to see how much I can get out of the car by driving like a nun.

Now I got myself a civic deisel 2.2 fuel economy better so is the acceleration



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Jocko

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Re: 29 mpg in 100% urban environment. Is this normal or what should I check?
« Reply #35 on: January 11, 2018, 10:27:36 PM »
The most I had on my mk 1 jazz was 47 mpg on the motorway and that was 40 mph and in 5th gear.
Wow! The worst I have ever had from my Mk 1 was 47.

eagle123

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Re: 29 mpg in 100% urban environment. Is this normal or what should I check?
« Reply #36 on: January 12, 2018, 10:16:20 AM »
The most I had on my mk 1 jazz was 47 mpg on the motorway and that was 40 mph and in 5th gear.
Wow! The worst I have ever had from my Mk 1 was 47.
Sorry I meant to say I got 53 mpg on the gf jazz

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eagle123

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Re: 29 mpg in 100% urban environment. Is this normal or what should I check?
« Reply #37 on: January 12, 2018, 10:16:59 AM »
The most I had on my mk 1 jazz was 47 mpg on the motorway and that was 40 mph and in 5th gear.
Wow! The worst I have ever had from my Mk 1 was 47.
Sorry I meant to say I got 53 mpg on the gf jazz

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Meant gd stupid autocorrect

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peteo48

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Re: 29 mpg in 100% urban environment. Is this normal or what should I check?
« Reply #38 on: January 12, 2018, 11:12:52 AM »
That's amazing Jocko - your worst is better than my average (44.5)!

peteo48

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Re: 29 mpg in 100% urban environment. Is this normal or what should I check?
« Reply #39 on: January 17, 2018, 03:28:39 PM »
Filled up yesterday. Just less than a mile back home. Have done a 1.7 mile trip today so 2.6 miles since fill up. Computer shows 36.5 mpg. Knock 10% off that and you have 32.85 mpg in real terms (ish).

Cold weather and short runs absolute killer so the 29 mpg in the OP is in the ball park for very short runs in cold weather and heavyish traffic.

plasma

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Re: 29 mpg in 100% urban environment. Is this normal or what should I check?
« Reply #40 on: January 17, 2018, 04:10:54 PM »
I always fill my tank to full. Until the first click off of the pump. The only way to get an accurate mpg figure is to fill the tank, zero the trip (or note the mileage - I do both), refill tank when fuel light comes on. Divide the miles covered by the gallons added to fill tank, and there is your mpg figure.

+1 yes that's how I allways do it.

Plasma

peteo48

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Re: 29 mpg in 100% urban environment. Is this normal or what should I check?
« Reply #41 on: January 17, 2018, 05:35:31 PM »
+2

I've heard it said that different pumps might click off earlier or later but, over several fills, this will give you your actual mpg.

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