Why So Far Out

[Doosan]

My on board computer reads 48 mpg, but when I do a brim to brim check It's more like 38 mpg. I reset everything each time I fill up and is still about the same. Is this normal to be 10 mpg out ? Dave

[Tony Barnsley]

Mine varies for some reason, it appears to be more oout at higher MPG's and then as the MPG falls so does the discrepancy . . at around an indicated 37mpg it agrees with a brim to brim check, at 47mpg it can be 5-6mpg out

[flyboyprowler]

There seems to be a lot of people on the forum with this "problem". The computers are known to be not too accurate, but with some being quite good.

Our 2 petrol cars are reasonably accurate, compared to a brim check, but apart from gratification or dismay, the info is not really a lot of use. Miles to empty would be a better thing, but neither of my cars have that.

[Tony Barnsley]

Miles to empty would be a better thing, but neither of my cars have that.

Mine does, but it is very pessimistic :( . . . Still much better than it being optimistic

[+Steve]

Do you guys think it has something to do with the cold weather? What is it like in the summer time?

[Davrav]

I find, on mine, that it varies depending on how full the tank is.........................

[NMaria]

My '07 reg was the same - showed about 10mpg more than it really achieved. My 'new' RAV, an 09 model, goes the other way, indicating about 42mpg when it actually does 46 or 47 mpg. My earlier petrol RAV was very accurate, and my husband's diesel BMW is also dead right. Just goes to show that it can be done.

[benxt5]

My 56reg xt5 d4d was the same as yours about 20% optimistic. My 62reg xtr is pretty much spot on, less than 1 mpg out either way.