How Accurate is the Avg. Miles Per Gallon indicator?

[Mr_Dobalina]

I just drove a 1,000 mile round trip in my 2007 4Runner with three windsurf boards and a cargo box on top of a Yakima rack. I also had 4 bikes on the back on a Thule rack.

The dash indicator said I averaged 19.4 miles per gallon for the trip. I can't believe this is accurate with a full load and two adults and 2 kids.

Has anyone ever manually checked the accuracy of this?

 

[BlackWorksInc]

There's been posts of it over the years; it all basically ends up in "mostly accurate... sometimes?"

I think we had a big theorycraft thread a long long time ago trying to figure out how Toyota calculates the mpg and such; but we never really settled on a consistent formula/theory.

The FSM has next to nothing in regards to how it works and how to check it's accuracy (which still extends to the newest models of Toyotas so "it's not reading properly" complaints are a pain.)

For example, I have 35's on my 4th gen V8 and I also installed a SpeedoHealer v4 to correct the speedometer (though technically not the actual vehicle speed signal output by the ABS module), my MPGs are generally 1+ real world calculations. i.e. in winter if it says I am getting about 13mpg, I'm usually getting closer to 12mpg. It does seem to become more accurate when I am on long trips/cruising. There's also the added possibility that it is averaging multiple tanks so you're looking an over all vehicle mpg and not tank to tank (though it does calculate your theoretical tank remaining.)

I'll see if I can dig up that thread.

 

[JONBOY345]

If you're stock, probably within an mpg or so...

Once big tires, armor, etc come into play, not very.

You can add the Speedohealer, I have added it to mine, and it improved some... But the computer is typically 1-1.5 MPG off.

If it reads 17 MPG, my hand calculation will be between 15.5 and 16 in 99% of instances.

 

[Mr_Dobalina]

If you're stock, probably within an mpg or so...

Once big tires, armor, etc come into play, not very.

You can add the Speedohealer, I have added it to mine, and it improved some... But the computer is typically 1-1.5 MPG off.

If it reads 17 MPG, my hand calculation will be between 15.5 and 16 in 99% of instances.

I am completely stock.

 

[Bossman]

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[Bossman]

https://www.toyota-4runner.org/872250-post5.html

There's been posts of it over the years; it all basically ends up in "mostly accurate... sometimes?"

I think we had a big theorycraft thread a long long time ago trying to figure out how Toyota calculates the mpg and such; but we never really settled on a consistent formula/theory.

The FSM has next to nothing in regards to how it works and how to check it's accuracy (which still extends to the newest models of Toyotas so "it's not reading properly" complaints are a pain.)

For example, I have 35's on my 4th gen V8 and I also installed a SpeedoHealer v4 to correct the speedometer (though technically not the actual vehicle speed signal output by the ABS module), my MPGs are generally 1+ real world calculations. i.e. in winter if it says I am getting about 13mpg, I'm usually getting closer to 12mpg. It does seem to become more accurate when I am on long trips/cruising. There's also the added possibility that it is averaging multiple tanks so you're looking an over all vehicle mpg and not tank to tank (though it does calculate your theoretical tank remaining.)

I'll see if I can dig up that thread.

 

[rdruss]

I just took my '03 V8 for a 40 mile highway run at 65mph cruise control setting and zero'd the mpg reader as I left the house, when I got back home it read 21.3 mpg, which makes me happy as it was reading 13.7 before I left after several short trips around town this winter. I also stopped on the trip turn around exit ramp and hand checked my tires for heat, all were cool to the touch, like room temp and it's about 65F here today. That makes me feel good too, as last fall I played around with SPC UCA and toe settings so I feel like I've got it in a good setting. Have not had an alignment and don't plan it.

 

[AuSeeker]

I never reset my avg MPG which never changed and my commute is always the same day in and day out, the avg MPG is always around 1.5 to 2 MPG more than my actual manually calculated MPG, so it's not very accurate IMHO.

 

[y=mx+b]

I reset it with every tank I fill up, and its consistently 2-3 MPG higher than actual. Even when accounting for the slightly taller than stock 265/70/17s

Its more useful for relative MPG. The display going up or down means the MPG is increasing or decreasing, but the number itself can't be taken at face value.

 

[MT Runner]

I reset it with every tank I fill up, and its consistently 2-3 MPG higher than actual. Even when accounting for the slightly taller than stock 265/70/17s

Its more useful for relative MPG. The display going up or down means the MPG is increasing or decreasing, but the number itself can't be taken at face value.

This.

I reset mine every tank. I keep track of my mpgs in the Fuelly app, I have kept track of every single one of the 137k miles I’ve put on it so far. And I have my speedometer calibrated for bigger tires.

The dash mpg is super consistent actually, it’s just high. It’s between 1.8-2.3 mpgs every single time.

So it’s still a very functional gauge, for me, I just take 2 mpg off what it says and I have a good idea of what I’m getting that tank.

Accurate? No. Consistent and reliable? Yes.