Fuel Consumption

[Bazile]

1. How is fuel mpg calculated on cars which displays this information .

2. Information display before purchase of fuel , says for example, 35 miles left from fuel in car .
You purchase x amount of fuel - display changes to 140 miles left for example .
How is the new figure of 140 miles left, calculated - what information does the car's computer uses ?

[Old_Geezer]

I suppose it has monitored how fast you use up fuel in the recent past an interpolates from that.

[bhg481]

The car's fuel gauge tells the computer how much fuel is in the tank; the average fuel consumption from the last few miles of driving is used to convert this into the distance drivable ie, miles per gallon * gallons = distance left.

[Bazile]

So , when the info display says your'e getting x amount per gallon - how frequently is that information being calculated ?

Does it say over the last mile you have used x amount of fuel and you have travelled x distance ?

[Old_Geezer]

I suspect it depends on the car. My readings are fairly consistent and slow changing. In my woman's car it is forever flitting from high to low values and back.

[bhg481]

Most computers offer two fuel consumption figures, average and instantaneous.
The instantaneous figure is calculated every 2 seconds or so using the odometer and the fuel gauge (or, more likely, the amount of fuel the injectors have been instructed to pump into the engine).
The average fuel consumption is calculated from the distance travelled since you last reset the computer and the fuel used since then.
The computer also keeps a record of the average fuel consumption it has calculated over the last 20 miles or so and uses this to estimated distance your car can travel on the fuel remaining in the tank. This can lead to the interesting situation where, if you've been driving in town with poor fuel consumption and then get into a clear driving situation, your estimated distance left can increase.

[Clanad]

From sensor "float" in the fuel tank. The amount of miles left are a simple calculation of your previous average fuel consumption maintained in the car's display computer...

Neither, by the way, are intended for any real degree of accuracy since the measuring device in the fuel tank, generally remains a simple float that moves up and down with the level of fuel. In fact, you'll probably burn 2 to 5 gallons (liters) before the gauge even begins to move when the tank is topped off as full...

[stocksman]

I put fuel in my car on the 19th Dec, and display said I had enough fuel for 193 miles. Today it says I have enough for 197miles. I have done 43 miles since filling up. I just wonder at what point will my tank overflow?

[ianess]

stocksman.....please post details [make, model etcetera] of your car. Most if not all of us want one like it.