Avg Mpg And Tank Avg Mpg...what Is The Difference As Such?

[grandb3rry]

Basically as you all know LExus IS220d has two sections with MPG, one: Average MPG and other being: Tank Average MPG. Now I know what the core difference is, where I seem to get confused which one is considered the main one? When everyone says I have 46.3MPG or 33.3MPG...which one you take the reading from?

I seem to be lost at the moment because after my last servicing few days ago (60k) tank average MPG has suddenly increased to 49.9MPG and then slowly dropped to 42MPG, but my Average MPG is always 36.7MPG. I have complained to Lexus about this saying that it needs the EGR valve cleaning, but they say they had a quick look and everything seems to be OK. Although they will contact me shortly (within few weeks) to arrange for the car's engine to be taken out and cleaned. Should this work be covered by Lexus?

Any thoughts will be appreciated!

Thanks

[new boy]

The average MPG is the average for the journey you are making or last made and can be zeroed by pressing and holding the reset next to the Speedo. Whereas the tank average is as it states the average of the fuel in the tank since last filling up. This zeros automatically when filling up and can not be manually reset. The figure you should therefore use is the tank average which is your actual MPG.

[Parthiban]

I think the tank average resets when you open the fuel door doesn't it?

[TigerFish]

The average MPG is the average for the journey you are making or last made and can be zeroed by pressing and holding the reset next to the Speedo. Whereas the tank average is as it states the average of the fuel in the tank since last filling up. This zeros automatically when filling up and can not be manually reset. The figure you should therefore use is the tank average which is your actual MPG.

Wouldn't it be the average between resets, rather than the journey you are making or just made? So if you never reset, that average would be more accurate than the tank average. So I guess the usefulness of either is dependent on how you use them, and how long you want the average over. i.e. neither is better than the other, just depends what you want to know.

To the OP, I assume if you reset the average MPG, while using the first tank of petrol it should pretty much mirror the Tank Average. After the second fill up, and as fill ups go by, it will settle and move slower as it measures across more miles and more fuel.

[fjcfarrar]

Basically as you all know LExus IS220d has two sections with MPG, one: Average MPG and other being: Tank Average MPG. Now I know what the core difference is, where I seem to get confused which one is considered the main one? When everyone says I have 46.3MPG or 33.3MPG...which one you take the reading from?

Any thoughts will be appreciated!

Thanks

The "tank average" is the best one for showing your current consumption, but is not at its best accuracy until about half a tank-full is used. Because car fuel flow transducers are not laboratory-type devices, their absolute accuracy is not great, so the mpg figure displayed can be 10-15% adrift from true mpg - but will be fairly consistent for a specific car. This means it is just a useful indication which can be used to see if mpg improves or worsens - or to help to drive economically.

For the true mpg figure, there is sadly no substitute for working it out by brimming the tank & noting the mileage, then after using most of a tank, noting fuel needed to brim it again and the miles travelled. Then if you want, you can calculate the number needed to multiply displayed mpg to get close to true mpg from then on.

[john8508]

The "How to increase your MPG " notice deals with the subject in a clear manner; but as I see it; the common sense answer should be the AVG should reflect the life average and the Tavg the current average. However, I fear we are not looking at the problem through Japanese eyes. Ah well, any more ideas?