Mpg Computer No Where Near Real Mpg

[Richard Martin]

Hi all,

I have recently purchased a 2003 Avensis tourer 1.8 T4 (the 2003-2009 shape). Had it a couple of weeks and have been very pleased with the figures for MPG that the computer is showing. I know they are never 100% accurate but I thought were pretty close or around 10% out.

Having done a few runs the average MPG figures were just not matching the range or even the recorded mileage. So yesterday as I had a long run with mixed driving, (A-Roads, Dual carriageways and motorways with the odd country lane thrown in for good measure) I thought I would do a brim to brim to check.

Anyway I did a round trip from petrol station to petrol station of 256.1 miles and filled brim to brim on both occasions. The total fuel used was 34.21 litres, which by my maths is 34mpg. Firstly I don't think that was overly great considering 75% of the driving was on the motorway but would be good to compare with others. Secondly the average MPG upon refilling was showing an average of 48mpg. A difference of 14mpg is huge, a 40% difference between real figures and recorded figures.

Is there anyway to get it more accurate?? From reading a few posts on here it seems most peoples aren't that far out from real figures.

[rockerbox]

Hi all,

I have recently purchased a 2003 Avensis tourer 1.8 T4 (the 2003-2009 shape). Had it a couple of weeks and have been very pleased with the figures for MPG that the computer is showing. I know they are never 100% accurate but I thought were pretty close or around 10% out.

Having done a few runs the average MPG figures were just not matching the range or even the recorded mileage. So yesterday as I had a long run with mixed driving, (A-Roads, Dual carriageways and motorways with the odd country lane thrown in for good measure) I thought I would do a brim to brim to check.

Anyway I did a round trip from petrol station to petrol station of 256.1 miles and filled brim to brim on both occasions. The total fuel used was 34.21 litres, which by my maths is 34mpg. Firstly I don't think that was overly great considering 75% of the driving was on the motorway but would be good to compare with others. Secondly the average MPG upon refilling was showing an average of 48mpg. A difference of 14mpg is huge, a 40% difference between real figures and recorded figures.

Is there anyway to get it more accurate?? From reading a few posts on here it seems most peoples aren't that far out from real figures.

First off - I'm afraid I don't have an answer. My Avensis - a 2.0 litre VVTi year 2000 model is wildly out also - but in the other direction. Four successive brim to brim checks for mostly local and often hilly terrain has revealed MPG's from worst to best - of 32.7 - 33.8 - 37.9 & 38.8. The last figure was with a particularly light foot. The indicated average MPG always hovers around 27 to 29 MPG and hardly ever changes during a trip even though it's supposed to update every 10 secs. The instantaneous MPG seems to vary in sympathy with load from 7 mpg up to it's limit of 99.9 mpg - which of course I have no idea is accurate. I would expect to get at least 45+ MPG on a decent run on generally flat roads not going above 60MPH.

There are no obvious indications that there is anything wrong. I only use the instantaneous reading nowadays as a guide to consumption - akin to the vacuum gauges used to provide a guide to 'economy' in days gone by. Hope you get a more helpful reply! Good luck.

[Richard Martin]

Thanks for your reply, it does seem an odd one. I knew mine was out when it was stating an average of 48 mpg but a range of 368, they just didn't match.

My average MPG on the computer does change constantly and the momentary MPG obviously updates all the time with a max mpg of 84.9, it won't go any higher than that.

[T5NELtim]

Hi,

I don't think 34 is that bad...

Best I have ever seen was 45 for a long motorway run (200 miles) doing an easy 65-70

Day to day drving I can get 39-40 which is within 10% of real figure (using brim technique)

I would love to know how it calculates this - perhaps there is a sensor fault or similar that can throw this out. In my case the range is well short of what I achieve.

In my wifes car range is clearly based on recent average mpg - not so with avensis as far as I can tell

Tim

[Richard Martin]

Thanks for the reply. Its hard to tell TBH if 34 is good or not as the astra was pretty good on fuel, but it was diesel, which is why I thought I could get some comparisons.

I do think it makes it even more disappointing that the computer MPG is so high, I would rather it showed it 28mpg and the real figures be 34mpg lol. I do think a 40% difference is quite big though and if thats the norm then its a pointless feature to have when its so inaccurate. I wonder if there is some setting (like tyre change) within the sat nav that is effecting the figures, but I don't know,

[t-spiritpete]

Hi all,

I have recently purchased a 2003 Avensis tourer 1.8 T4 (the 2003-2009 shape). Had it a couple of weeks and have been very pleased with the figures for MPG that the computer is showing. I know they are never 100% accurate but I thought were pretty close or around 10% out.

Having done a few runs the average MPG figures were just not matching the range or even the recorded mileage. So yesterday as I had a long run with mixed driving, (A-Roads, Dual carriageways and motorways with the odd country lane thrown in for good measure) I thought I would do a brim to brim to check.

Anyway I did a round trip from petrol station to petrol station of 256.1 miles and filled brim to brim on both occasions. The total fuel used was 34.21 litres, which by my maths is 34mpg. Firstly I don't think that was overly great considering 75% of the driving was on the motorway but would be good to compare with others. Secondly the average MPG upon refilling was showing an average of 48mpg. A difference of 14mpg is huge, a 40% difference between real figures and recorded figures.

Is there anyway to get it more accurate?? From reading a few posts on here it seems most peoples aren't that far out from real figures.

Have you reset the MPG computer since you bought the car?

Pete.

[Richard Martin]

Is there way to actually reset it?? Every time I refuel the MPG calculator resets itself to zero automatically along with the range, regardless of how much fuel I put in.

[Jas16]

thats not too bad for a 1.8, but what I have found that if I do a 50:50 mix then the computer MPG average is closer to the real, compared to the other extreme which is doing a solo motorway run which would highly inflate the figure, for example, I find it hard to believe that my 2.0D4D does almost 70mpg at 65mph average over 170 miles down the M1.

On the other hand I am quite surprised with how much the difference is between the figures, I would have agreed with your estimate of within 10%. If this happens all the time then it could be an issue with one of the sensors used to calculate the MPG in the first place, although I have no idea how it does calculate it so am not of much help there

Or you could just accept that it is what it is and carry on, if the car is driving fine and there are no issues

[Richard Martin]

Would you accept it if your speedo was out by 40%, or would try and see if the issue could be resolved?? Its redundant if its that inaccurate, 10% tolerance is ok but 40% is ridiculous, its a 200 + mile difference per tank, that's huge.

This was a mix of driving with around 160-180 of the miles being motorway. On the motorway the average on the way up was around 34mpg which would have been pretty accurate, on the way back it steadily climbed to 48mpg.

I have had the computer upto an average of 55mpg on a 50 mile A road trip, which I really doubted at the time. It would be interesting to know how its getting these figures. I would say its clearly not using a sensor in the tank or measuring fuel used, I suspect its calculating it from revs and speed, with no sensors.

[Jas16]

Have you spoken to a dealer about it, and has the car been serviced by yourself? or Toyota?

Personally, I do my mpg by brim to brim so don't really care about car computer. I gave that up when my Focus was telling me I was doing 90mpg at 60mph pure motorway and when I checked brim to brim, it was more like 60mpg, admittingly not quite 40% but enough me to loose most faith in these values, however the Avensis in general has been out by, at most 20%.

As I said previously, I find it more accurate the greater the amount of town driving one does,

Saying that, as my driving amount and routes don't change much ie same journey most of the time, I have a pretty good idea how much I should get out the tank, ie by half way I would have done about 350 miles with the light coming on around 600

[MacPlumb]

Yes they are not very accurate. I had a 2003 T2 1.8 VVTi for 7 years. The indicated consumption was rarely less than 52 mpg but on a long run of say 200 to 400 miles it would show up to 72 mpg!

I would often check the consumption from full to full and this would typically be between 36 and 44 mpg.

So a big difference between indicated and calculated. I would aim to get at least 400 miles between fill ups, best ever was 525 miles. Pretty good for a 1.8 but I do try quite hard to save fuel.

Using Fuelly.com my 2003 model was better than my 2010 by a couple of mpg, although this is comparing 5-speed manual with CVT. The gauge in the newer model is very close to the actual consumption.

[Richard Martin]

Yes they are not very accurate. I had a 2003 T2 1.8 VVTi for 7 years. The indicated consumption was rarely less than 52 mpg but on a long run of say 200 to 400 miles it would show up to 72 mpg!

I would often check the consumption from full to full and this would typically be between 36 and 44 mpg.

So a big difference between indicated and calculated. I would aim to get at least 400 miles between fill ups, best ever was 525 miles. Pretty good for a 1.8 but I do try quite hard to save fuel.

Using Fuelly.com my 2003 model was better than my 2010 by a couple of mpg, although this is comparing 5-speed manual with CVT. The gauge in the newer model is very close to the actual consumption.

Thanks for the info its been helpful.