On Board Computer Accuracy

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Sun 29 Aug 2010 13:26
On Board Computer Accuracy - bintang

My tank holds 11.60 gallons. The computer shows 43 mpg. This would give 499 miles. When I fill it to the brim, the computer tells me I have enough fuel for only 405 miles. What is going on?

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Sun 29 Aug 2010 14:07
On Board Computer Accuracy - Xantiaman

Can't comment on the range issue. But my car's computer underestimates my MPG. It tells me the car return an average of roughly 43.5mpg. As I usually brim the tank, I know the actual return varies between 46 to 47mpg.

Not sure how the computer calculates range and consumption but presume it cannot do this with complete accuracy.

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Sun 29 Aug 2010 14:55
On Board Computer Accuracy - Armitage Shanks {p}

SFAIK the computer calculates your range based on the fuel consumption you have achieved in the last 30 to 40 miles you have driven. This can lead to errors!

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Sun 29 Aug 2010 16:34
On Board Computer Accuracy - colinh

"...calculates your range based on the fuel consumption you have achieved in the last 30 to 40 miles..."

Maybe the theory, but in my previous car, a Golf, it could vary wildly depending on every up and down in the road. Could be very misleading on a long descent by showing 100+ miles and then you got to the bottom and on the level, and would then show less than 20.

My current cee`d doesn't increase the range when descending, and does seem to take a longer-term average

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Sun 29 Aug 2010 16:50
On Board Computer Accuracy - Armstrong Sid

Surely you can get both, depending on your settings which can be user-adjusted. At least on my Focus you can.

So I recognise both scenarios which people have mentioned here. I can set it to show me the average consumption I've had over the last 30/40 miles; or I can set it to show me the instantaneous figure where I've seen anything from 0-99 mpg

Edited by Armstrong Sid on 29/08/2010 at 16:50

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Sun 29 Aug 2010 17:19
On Board Computer Accuracy - Xantiaman

Surely you can get both, depending on your settings which can be user-adjusted. At least on my Focus you can.

Yes, my Signum shows instantaneous figure along with two averages. I haven't changed one since getting the car so that shows an average calculated over 50,000miles.

I don't take the instantaneous figure at face value, but get a flat stretch of road put the car on cruise control and it really demonstrates the better consumption achieved by dropping 10mph off your speed.

Edited by Xantiaman on 29/08/2010 at 17:19

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Sun 29 Aug 2010 19:42
On Board Computer Accuracy - bathtub tom

I use mine as a rough guide. Using the 'fill to brim' method, the difference between the on board computer and calculated figures can vary by more than 10% either way.

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Mon 30 Aug 2010 10:37
On Board Computer Accuracy - Roly93

I,ve never tested the remaining mileage part of my Audi on-board computer, but the MPG is pretty accurate compared to a brim to brim measurement, I'd say within .5mpg.

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