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      10-28-2006, 04:50 AM   #1
red355
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OBC MPG accuracy

For those of you that are anal enough to record information on the fuel you put into the car, how accurate is the OBC figure?

Last three fill ups have shown the following margin of error which is I think is a good as we can expect.

+0.85MPG , +0.64MPG, +0.64MPG

which is an average error of 1.78% over 1350 miles... or about 2.2 litres or 1/2 gallon

Typically other cars I have driven over that last ten years have tended to be between 5-10% optimistic

yes I know thats its very sad that I have worked this out.
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      10-28-2006, 06:02 AM   #2
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From my (not so accurate ) calculations I've been seeing the OBC read about 1 - 2 mpg high. Reading, say, 43.4 when I've been getting aroun 41-42. I've not worked it out for the last few tankfulls though.

I wonder if it depends on what type of driving you do as to how optimistic it is. If you have even more spare time on your hands you could track accuracy for each tank full against % spent for each tank doing motorway/town/rush hour, and maybe work it out!
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      10-28-2006, 11:23 AM   #3
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Quote:
Originally Posted by JonMad
From my (not so accurate ) calculations I've been seeing the OBC read about 1 - 2 mpg high. Reading, say, 43.4 when I've been getting aroun 41-42. I've not worked it out for the last few tankfulls though.

I wonder if it depends on what type of driving you do as to how optimistic it is. If you have even more spare time on your hands you could track accuracy for each tank full against % spent for each tank doing motorway/town/rush hour, and maybe work it out!
That's not being anal, that's getting all the way up into the small intestines.
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      10-28-2006, 11:54 AM   #4
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Quote:
Originally Posted by JonMad
From my (not so accurate ) calculations I've been seeing the OBC read about 1 - 2 mpg high. Reading, say, 43.4 when I've been getting aroun 41-42. I've not worked it out for the last few tankfulls though.

I wonder if it depends on what type of driving you do as to how optimistic it is. If you have even more spare time on your hands you could track accuracy for each tank full against % spent for each tank doing motorway/town/rush hour, and maybe work it out!

41-42!!!!!!!!!!!!!!!!!

Man, must be nice. I get just over 30, on a straight highway cruse, like maybe 32.

Matt
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      10-28-2006, 11:54 AM   #5
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Quote:
Originally Posted by SoYank
That's not being anal, that's getting all the way up into the small intestines.
However i was being paid a substantial amount of £££ whilst I worked it out?

waiting for 36 GB sybase DB to back up.
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      10-28-2006, 12:45 PM   #6
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Quote:
Originally Posted by ///Matt
41-42!!!!!!!!!!!!!!!!!

Man, must be nice. I get just over 30, on a straight highway cruse, like maybe 32.

Matt
Apples and oranges ///Matt. His mile is the same as your mile but his gallon is 25% more than yours.
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      10-28-2006, 02:29 PM   #7
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Due to the amount of motorway driving I do, my OBC regularly tells me I've done an av of 50 mpg. However, brim to brim it's more like 48 mpg (although I've not been anymore scientific than that)
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      10-30-2006, 05:43 AM   #8
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Last tank, OBC again 2mpg above reality (said 47, got 45).

Just for Matt..
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      10-31-2006, 10:07 AM   #9
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OBC reads about 2mpg (UK gallons that is) or about 5% lower than what I measure brim to brim. My 1997 Nissan Primera GT got within 0.5mpg evertime.
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      10-31-2006, 11:44 AM   #10
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Mine OBC are a bit more optimistic then real MPG
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      10-31-2006, 11:54 AM   #11
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My OBC also shows about 2-3 mpg optimistic. My last tankfull showed 50.3 on obc and because of very slow long drives i had been doing (trying to get back to London from Cornwall) the actual mpg was 49.x. I had done 457 miles and could only get 42 litres in.
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      11-16-2006, 03:07 PM   #12
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Last two tank fulls have been with Ultimate diesel..its had no impact on average MPG sitting at just under 40 mpg.

However I do think the car runs smoother....or is that the effect of another 1000 miles under its belt?
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