Accuracy Of Mpg Computer

[Krait]

I have an 07 1.6 petrol and I have never believed in the accuracy of the computers. But I was very surprised the other day. I reset the Average Mileage when the display changed to indicate I was on reserve. I later filled in 46 litres. As you know this approx. 10 gallons (4.546 litres)

When the Reserve came on again I had covered exactly 418 miles and the Average MPG showed 41.6.

Most surprised and pleased.

[farika]

41.6 MPG with 124 Auris 1.6 VVTI? !

I have the same auris, but I've never dropped below 34.09 MPG ... (100km / h - 110 )....

I even have the 29 MPG @ 130kmh.

How you do that ? Unless it's me who has a problem but everyone told me that my consumption was normal. On spritmonitor i'm on average.

[Daveyonthemove]

I wouldn't take it too seriously as it wasn't worked out in an accurate manner.

[Jarod]

41,6 possible but not fun to drive ehh. My record is 47 - but that was driving 50mph no cities no accelerating, no braking

[ptaurissr]

I get average 42 mpg (even with lead foot!) on my 134 valvematic although that is a 6 speed manual

[farika]

42 mpg with lead foot? ... I don't know how you can have this very low consumption... Okay it's the new valvematic , but Kraig have a good consumption too and i have the same engine...

7.6L/100 @ 110kmh yesterday !!! with speed regulator... SP95...

[Krait]

Very easy. I did about 200 miles of that on the M4 with cruise set at 65mph.

Try it. It definitely worked. After this test, I drove at a steady 90mph and still recorded average mileage at around 40. Maybe I'm doing something wrong???

After driving a Mazda 6 sport for 4 years I have to lose the lead in my shoes as it does not have the same effect.

Daveyonthemove. Pease explain how I can be more accurate. When the reserve switch operated I zeroed the miles. Filled in 10 gallons and then checked when the switch activated again. Short of emptying the tank, filling in a fixed amount of petrol and then driving until empty of course.

Car is due for its 60k service in 10 days.

Seems I may be doing the right thing.

[Daveyonthemove]

Very easy. I did about 200 miles of that on the M4 with cruise set at 65mph.

Try it. It definitely worked. After this test, I drove at a steady 90mph and still recorded average mileage at around 40. Maybe I'm doing something wrong???

After driving a Mazda 6 sport for 4 years I have to lose the lead in my shoes as it does not have the same effect.

Daveyonthemove. Pease explain how I can be more accurate. When the reserve switch operated I zeroed the miles. Filled in 10 gallons and then checked when the switch activated again. Short of emptying the tank, filling in a fixed amount of petrol and then driving until empty of course.

Car is due for its 60k service in 10 days.

Seems I may be doing the right thing.

Unless i misunderstood your explanation, then you filled the car up when the red light came on the first time, and then when it came on again, you made a note of the mileage and worked out the MPG from that?

If this is the case, then it is inaccurate for a couple of reasons.

1) Unless you were at a filling station the exact time the red light came on, then you had to have driven it a few miles to get to one soon after it came on, meaning you don't know for sure how much fuel you have used after the red light came on.

2) The low fuel warning is subject to gravity. For example, if i park on my drive with the nose facing downhill I can gain 1 bar of fuel and if i park with my nose facing uphill i can lose 1 bar of fuel, meaning that the fuel light could come on early when I have more fuel in the tank than it thinks, or less depending on how i park. This makes your method subject to too many variables.

The most accurate way to work out your MPG is to fill the tank to the absolute brim and put the cap on.

Reset your mileage and your average MPG if you wish to compare.

Drive as far or as short as you want to and then fill up to the brim again.

Now work out your MPG from the litres you put in the tank and the distance travelled.

This is more accurate because there is no way you can put more fuel in if you fill to the brim, so you know the exact amount of fuel that was used. Filling up to the 'click' at the pump is also inaccurate because different forecourts have different gradients, different pumps deliver fuel at different fuel rates, and the click could vary simply on those variables.

Hope that helped.

[farika]

I have a much higher consumption of gasoline ... Where this might come? Car with 30,000 km. At 90 MPH I have about the 28 MPG! I never dropped below 35MPG whatever the conditions.

Issue on my engine ? :/. Toyota said "all is normal"

[farika]

"duplicate"

[Krait]

Hey DOTM,

You are not reading the message correctly.

1) When the reserve is activated I reset the mileage. So I do not have to be at the pump to fill in at this time.

2) I fill in exactly 10 gallons. This amount saves me making any calculations when the reserve light is activated again.

Granted, one error that can occur is due to inclination of the tank. However, keep testing in this way and accumulate an average over time and distance and you will have a much more accurate reading.

Other, more significant errors are:

Driving style

Terrain - motorway or suburban.

Terrain - flat or up hill and down dale.

And so on.....

Or you can believe the specification from the manufacturers.

But I am still quite surprised at the differing MPG's from all of us.

Cheers

[Daveyonthemove]

I understand a bit better now, and your method does seem more accurate now you have explained it, but I still believe that it's not as accurate as brimming it and then working out the mpg from there :)

[Krait]

I'm just a lazy sod and this seemed the one with least hassle.

What surprised me was that the Auris fuel tank capacity is supposed to be 12.5 gallons (approx) according to my User Manual!! When the reserve comes on I cannot fill in 10 gallons. I have to drive around 20 miles and then I can. Which implies that when reserve is activated we have about 2.5 gallons!!!!

You'r right, I am not going to test that.

Cheers

[ptaurissr]

Yup the reserve is about 2 gallons which is a bit mental, I can still do circa 80 miles after the light first comes on!

[Daveyonthemove]

Toyota claim that this can be reset to improve accuracy.

I'm sceptical.