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Discussion Starter · #1 ·
Have done a search - but couldn't find anything...

Went to fill up the car in my lunchbreak as it was low on fuel & on the way to work this morning there was a queue so drove past instead.
Anyway - on the way there at lunchtime (all of 2 miles) it read 42.9 av mpg which is about usual (am in UK).

Edited to add - it was not 'low' but it was just under 1/4 tank - and as we have snow forecast & lots of commuting, I thought it prudent to pop more in! it was also -1 at the time

After filling, I went up the road & round roundabout - glanced at the reading & it was showing 30.1! :cry:
Drove back the 2 miles & during that drive, it shot up in 2 mpg increments and eventually ended up at over 50.6 mpg........ all in the short space of less than 2 miles! When parked, it was still showing 50.3

On driving home tonight it read 48.1 from starting up & for much of the journey (never reads that when am on the commute!) I did phone dealer at lunchbreak (Useless bunch) and they said they would note it down but I could reset the trip to see if that made a difference - by twiddling the button by the reading on the dash......muppets!
I ended that call by them promising to phone me this afternoon with info (or not) about it...... no call.....

Anyone had this sudden shift of mpg reading?:confused:
 

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Might it be on reset every time you fill up? Mine is set to reset trip on fill up, not sure if this resets mpg, but just a thought :)
 

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^Yes you can. The process is in the manual.



This happens every time I fill up. I have my Trip A odometer and fuel MPG set to reset every time I fill up. The Range and MPG numbers jump all over the place (high and low) for the first 20 miles depending on how I am driving.

Nothing to be worried about IF you are resetting your odometers/meters
 

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Discussion Starter · #6 ·
Might it be on reset every time you fill up? Mine is set to reset trip on fill up, not sure if this resets mpg, but just a thought :)
ta for the idea, but no - its not set for re-set each trip.
Its never happened before - maybe a slight slip of .2 or .3 but never such a huge change like I had today - am baffled!
 

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ta for the idea, but no - its not set for re-set each trip.
Its never happened before - maybe a slight slip of .2 or .3 but never such a huge change like I had today - am baffled!
Wow, only .2 or .3? you have a feather foot then :p

I've seen between high 40s & nearly 30 depending on the reason for the drive, business or pleasure.
 

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Discussion Starter · #8 ·
Wow, only .2 or .3? you have a feather foot then :p

I've seen between high 40s & nearly 30 depending on the reason for the drive, business or pleasure.
aww, I've seen it veer downwards when I've been a bit lead footed :pP: - but not on the commute or when filling mister - hence the question as its so out of 'character' to do this
 

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I was wondering if you had tripped a run-in point in terms of mileage and it had switched to a more ecconomical ECU mapping, but if it's back to normal, maybe not. I guess maybe a maths rounding error in calculating the display value (with some unlikely numbers causing the error to persist)
 

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every time you reset your trip odometer, trip A let's say, it resets the MPG counter. for the first 50 miles or so it can jump around. coasting and cruising low speed will cause it to increase dramatically, and any type of acceleration will cause a dramatic decrease, but especially hard acceleration.
 

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Yes, I got something similar. Started the day with {A} reading 48.9mpg /93.5 miles. Long defrost (from -11 celcius), and trundle out of the village. 3 or 4 miles later, I saw 34mpg and though it had dropped off quite a lot! Within another 5 miles, it was back at 47.x. I'd definitely put my money on some maths going awry in the calculations.
 

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THe default setting on your Trip A is to reset back to 00 when you put gas in it. During the first 100 miles or so, you are going to see a drastic change in MPG since it only has a few miles to calculate against.

Where it really matters is probably after you get down to a half tank or so and you will see it takes a bit longer to increase or decrease MPG. This is because it has 150 miles of driving or so to calculate against. Page 87 goes into a little more detail.
 

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THe default setting on your Trip A is to reset back to 00 when you put gas in it. During the first 100 miles or so, you are going to see a drastic change in MPG since it only has a few miles to calculate against.
This is, frankly, nonsense. For the first mile or so, the MPG may vary, but with 10 litres or so of petrol and 100 miles, any measurement errors should only show the MPG changing by a percent or so.

It is easy to check this - watch the gauge as you drive steadily, and it only moves by 0.1 MPG at a time, not in 5MPG jumps.
90 miles, 34MPG = 2.65 Gal
95 miles, 47MPG = 2.02 Gal

If they have this written in the manual, they KNOW they have a software bug.
 

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i see mine change from 43 to under 38 within a 25 mile trip. the only time it changes less drastically is after the trip has gone over 200 miles, and my driving remains consistent. the following will cause a drastic swing: low trip mileage (under 150 miles i would say) combined with changes in temperature, and driving patterns. if you baby it your MPG will be very high, if you then romp on it on your next trip, your MPG will drop DRASTICALLY.
 

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Capt'n Jack
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This is, frankly, nonsense. For the first mile or so, the MPG may vary, but with 10 litres or so of petrol and 100 miles, any measurement errors should only show the MPG changing by a percent or so.

It is easy to check this - watch the gauge as you drive steadily, and it only moves by 0.1 MPG at a time, not in 5MPG jumps.
90 miles, 34MPG = 2.65 Gal
95 miles, 47MPG = 2.02 Gal

If they have this written in the manual, they KNOW they have a software bug.
No software bug. You can get fairly large swings up until 100 miles or so. But yes, the most swings are probably under 50 miles. After a trip "A" reset drive it 10 or 20 miles. Watch the MPG meter change as you coast to a stop, excellerate, go up a hill etc. Continue watching the swings until it does start add/detracting in 10ths which is usually around 100 miles (OK 90 or 95 in the above case) This nothing out of the ordinary. My last 3 vehicles have had MPG indicators. As with any mathmatical formula or logic, the more information that is available (in this case miles verses fuel use), the more reliable the calculations. What counts is the MPG when you refill the tank or you can of course use "B" trip to see longer MPG stats if you have not reset. I use trib "B" for seasonal gas mileage. Got into that habit with the 07 Civic Hybrid.

Of course, terrain, driving habits etc can play a part.
 
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