That's an interesting site (fuelly.com), it will be great to compare our vehicle against others, cool!
I find a simple and quick way to get mpg is to use the OBD2 connection, if the car has one that is..
A cheap sensor like
in combination with a program
on your android phone or tablet will enable you to get a quick mpg by taking the car for a 5 minute spin before and after.
You can get the apps for apple phones and laptops as well.
The programs allow you to set up multiple cars and it will keep records over time so you can see changes and true averages.
There is likely to be a margin of error but it will be the same on both trips giving a fairly good idea to what the improvement is.
Unfortunately it will sometimes take up to a few tanks of fuel to get the full effect but then you can do it again after that has been done.
It's also very useful to check error codes and resetting them so the dashboard engine light turns off.
This can be quite impressive to the customer and obviously useful to us
Don't forget to remove the sender when you're finished! It's easy done
. Tie a colorful ribbon or something onto it..
To calculate the percentage gained, deduct before from after (24mpg - 18 mpg = 6mpg gained)
Then calculate the gain using the original mileage and the gain i.e. 6 / (18/100) = 6 / 0.18 = 33.33333 % mileage gain.
I see someone has put in a car since I put the first lot in, very cool!
It only takes a minute to do and will be really helpful for everyone so please, pop them in!