MPG at Idle drops to 8.5MPG

mingblus3

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When I start the car the MPG display starts at 19.5 and then starts dropping down and then settles at 8.5MPG or thereabouts. Is this right?

Terrible if this is right, and on a run the max i've seen is 21.1MPG, any chance a service might help, it's coming up to the next A service!!

C32 AMG.
 

S80

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None at the monent, but there's an OM642 in the Jeep Grand Cherokee!
With the car stationary, a 'MPG' figure is meaningless.

Are you sure the display isn't reading fuel usage in 'somethings' per hour, then switches to MPG once a certain speed is reached?
 

television

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When I start the car the MPG display starts at 19.5 and then starts dropping down and then settles at 8.5MPG or thereabouts. Is this right?

Terrible if this is right, and on a run the max i've seen is 21.1MPG, any chance a service might help, it's coming up to the next A service!!

C32 AMG.

This weather my SL500 starts at 4.7 mpg,,but still returns up to 30 depending on how you drive it
 

S.Speed

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Dont forget that the very worst MPG figure is at stand still because you are actually doing zero mpg !!
 

kristoff

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If you're getting 8.5mpg at idle then you are being towed.
 

television

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It cannot show zero as it can only show MPG so it shows what you would be getting if you were moving, purely on the same principle that if you were doing X MPG and you get stuck in a jam,,the it will count down the whole time that you are stationery, and that is the only way that it can be
 

S.Speed

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Its still ZERO mpg at ZERO mph though..
Facts are facts !
 

AndrewIles

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The worst mpg I have seen in my C32 is 20mpg and the best 28mpg.

That's after 18 months and about 20k miles.
 

Miffy

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well yes, it is ZERO if you dont move, but once you have covered a small distance, its now taken as an average
 

Tashman

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So its "average" mpg, not "instantaneous" mpg
My mum's focus has a function to read both
 

television

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So its "average" mpg, not "instantaneous" mpg
My mum's focus has a function to read both

No it is real time, while the engine is running, they are all near enough spot on. if you are stopped in a jam you can turn off, to stop it from counting down. Just because you are stuck in traffic the car does not know this.
To have the display read X amount of liters per minute would not go down either
 

Miffy

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mine is not real time. My mondeo had real time and avg. When in realtime mode, if I went down a hill using engine braking, it would rise to 99mpg, and if I accelearted hard up a hill it would drop as low as 8mpg. In fact any hard acceleration would show in the MPG straight away.

In my clk, it starts off at 22, if I get onto a motorway and stick at my normal spedd circa 70sih lol, then after a while it will rise very slowly, 22.1 22.2, 22.3 etc until it gets to its peak at around 32 if I am lucky, then at the end of the journey, it will start to drop very slowly at a similar rate, so it is deff displaying an avg mpg and not realtime
 

jberks

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Mine starts at 40mpg and by the time I've backed out of the drive, 30 secs later, is showing something like 32. Sat at idle it will easily drop to early 20's and thats a diesel. I frequently see my Dad's E220cdi showing 23mpg as he probably sits outside shops waiting for my Mum and then stop/start to the next one.
I hit the motorway reading maybe 30mpg, 30 miles later its maybe 38 but if there's a couple of miles of 50mph limits or an opportunity to coast for a mile to slow down and I can get that up to 43 or more. Its an average so a couple of miles using virtually no fuel over a 50 mile run can make a massive difference, just as a mad 5 mins at 100 can.
Do 200 miles and coast for a mile and it won't even notice.
 

Tashman

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So its average mpg then.
When stationary with the engine running your 'instantaneous' mpg is Zero.
If the figure displayed starts to slowly drop while you're stationary then it is displaying average mpg.
 

busby20

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Mileage?? who cares, what's the point in having a fast quality car.....then worrying about the MPG? :twisted::twisted:
 

Tashman

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Whats ur avatar?
An Opel Manta?
 

busby20

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Whats ur avatar?
An Opel Manta?
Yes, it was a "special" tuned 400 that belonged to my son - it was featured in Fast Car magazine and was on the front cover:)
 

whitenemesis

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Yes, mpg is a running average, constantly updated. When stationary it will slowly drop, eventually reach 0mpg (no idea how long you must be stationary!)

At start up it displays the the last measured average, dropping quickly to the current value.
 

television

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Yes, mpg is a running average, constantly updated. When stationary it will slowly drop, eventually reach 0mpg (no idea how long you must be stationary!)

I think that I could achieve 0 mpg after 10 mins :D:D
 

jberks

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It must be programming to some extent. Mine is down to 29ish by the time I'm on the main road, then creeps back up. Swapped with the old man for a day last week when he kindly took mine in for tracking and new tyres. Backed out of the drive and it was reading 22mpg!! By the time I reached the main road it was reading 18!
Not great for an E220cdi.
Overall though, when I'd got to work, it was fractionally better than mine .
 


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