DIYbanter - View Single Post - What is the realistic accuracy & precision of typical consumer MPG calculations (tripmeter miles/pump gallons)

Frank[_24_]

On 7/20/2017 9:04 AM, wrote:
On Thu, 20 Jul 2017 12:08:33 -0000 (UTC), Mad Roger
wrote:

What is a realistic accuracy & precision of typical MPG measurements when
measured by the consumer using the typical method of dividing their
tripmeter miles by the gas-pump gallons during fillup?
Repeatabilty is terrible. Accuracy can be pretty good over multiple
tanks. Can be pretty good even on single tanks IF there is a way to
ensure the tank is always filled to EXACTLY the same point (like a
level in the fill - tube, with the vehicle parked at EXACTLY the same
place for each fill-up). Relying on the auto-shutoff of the pump can
cause variance of several liters per fillup.

My year old car gives constant mileage and appears very accurate when I
calculate based on fill-up. It even has a moving mileage meter going up
to 80 mpg when just coasting down hill or maybe 10 mpg going up hill.
I recall many times on long trips mileage varying all over the map
probably because I was filling up at different stations.