Yaris fuel economy query

[Malcolm Preen]

One of the reasons for getting a Hybrid car was fuel economy.... but I've got an oddity...

The 2022 Yaris has all sorts of Fuel Economy settings.... trip, tank and overall... No problem with that... but I'm wondering...

Typically, I fill the tank, note the mileage done on the previous tank... and record the details in my spreadsheet...

I filled up today, after a few long journeys.... 440.1 miles on a full tank... 27.22 litres (6 gallons) - approximately 73.35 mpg

Yet, the car reports that the "Tank" economy is 80 mpg

I accept that the tank may not have been filled to the exact same level.... but over the four months I have had the car, I see a similar pattern each time... with the overall average coming in at about 77 mpg

I fill up at various filling stations, so I doubt the problem is related to the pump measurements...

Maybe I'm being paranoid.... but it feels to me like the numbers reported by the car are "less than accurate"

Thoughts?

Malcolm

[CPN]

You are right. The dashboard readings are over optimistic by a factor of approx 10% in most cases. 

[Trewithy]

Different brands of fuel seem to froth at different rates causing the pump of click off at slightly different tank levels.  If you like to keep a track of fuel consumption then it is best to always fill at the same fuel station and if possible at the same pump.

[CPN]

I never go by the "click-off" level when I'm filling up and always keep going past that until it fills up the down tube right up to the lip. It's the only way to be consistent and accurate every time, no matter where I fill up... (and yes, I know that will annoy anyone waiting behind me 😉)

[Roy124]

CPN, there was discussion about brimming some time back. I can't remember the details but it was to do with the vapour filter and the potential for contaminating it.  As I say, I remember her an issue.  The advice was not to fill beyond first click.

For accurate consumption you only need fuel in and mileage and the first click level should not vary significantly. As far as the car display, 'frothing' will result in less fuel to first click but the on-board calculation should not be affected.

[CPN]

Ok, I get the point but I never actually let it get to the brim to avoid spillage but probably about 2 inches in from the edge so that I know it's the same every time.

[Cyker]

It's a known thing, not just with the Mk4 but all Toyotas with an mpg gauge. Come to think of it, pretty much all manufacturers cars I know of have roughly similar errors between computer and calculated mpg rating.

I tend to take it as a rough guide rather than absolute because of this!

I get similar discrepancies between calculated and computer mpg.