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# How am I supposed to work out the MPG of my car ? watch

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1. I thought the best way was too fill your car to a full tank and then drive until your fuel light comes on, then measure how many litres you used.

So I did that and it took 40 ltrs to fill my car and I got 370 miles. but my fuel tank capacity is 52.3 ltrs for my car ?

People on TSR (inc mackemforever) said the gauge doesn't read accurate.??????
if that is the case, how am I supposed to work out my mpg ?

Also, if what he is saying is correct, he is saying when my fuel light comes on I should be able to drive another 130 miles because the gauge is wrong !!!!!
I don't believe that
2. Fuel gauges on cars are never accurate, not even on the best cars!

The best way is to either fill your tank up to the top and only refill once its gone down to the first mark down eg the 3/4 full mark.

2) Refill to top noting how many litres you put in and what mileage you did since you last filled up.

3) Do this 3 times and get the average number of litres used by adding the litres each time and divide by 3. Eg if it takes so 7litres each time then that's 7 +7+7= 21 21 divide by 3 is 7

4) So you have average number of litres. Now convert that to gallons. 7 litres is 1.54 gallons. You can do the conversion online by googling convert litres to gallons!

5) do the same with your mileage each time. subtract the previous mileage from latest mileage to give you miles done since you last filled up. Add them together and divide by 3 to give you average number of miles done.
E.g 45190-45065 do this calculation each of the 3 times you fill up. So let's assume first refill 125 miles. second is 112 miles. third is 105 miles
125+112+105=342 342/3=114

6) divide average mileage by average gallons used. That will give you miles to the gallon.

MPG= Average number of miles done/ average gallons used

114/1.54=74 mpg
3. (Original post by Ambitious1999)
Fuel gauges on cars are never accurate, not even on the best cars!

The best way is to either fill your tank up to the top and only refill once its gone down to the first mark down eg the 3/4 full mark.

2) Refill to top noting how many litres you put in and what mileage you did since you last filled up.

3) Do this 3 times and get the average number of litres used by adding the litres each time and divide by 3. Eg if it takes so 7litres each time then that's 7 +7+7= 21 21 divide by 3 is 7

4) So you have average number of litres. Now convert that to gallons

5) do the same with your mileage each time. subtract the previous mileage from latest mileage to give you miles done since you last filled up. Add them together and divide by 3 to give you average number of miles done.

6) divide average mileage by average gallons used. That will give you miles to the gallon.
Woah ! I have Dyspraxia and I find that to be VERY VERY confusing !!!!!!!! I've enver heard of doing it that way before

So, what is happening to my other 13 litres of fuel ?
4. I've already told you before, I'm pretty sure, just set up and account with Fuelly. Each time you fill up you just type in the numbers and it does all the maths for you. You can either do it with trip miles (and reset it each time you fill up) or with odometer miles.

Your extra fuel isn't going anywhere, it's just sitting in the tank. Most red lines/fuel lights are pretty conservative, otherwise idiots would be running out of fuel all the time and blaming the car maker for not making it more obvious. I refill mine whenever I get to a quarter of a tank. Three of my cars didn't have fuel lights - from the factory mind - so you just had to fill them when they got low. My current car has a fuel light and a little bong noise when it comes on but it's only happened once. If you want to utilise the rest of the fuel in your tank then it's time to start getting lucky, especially as diesel systems are a PITA to prime if you run out of fuel.

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Updated: November 9, 2015
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