Mismatch between real gas consumption and average indication

[calin]

I just bought a 2004 Toyota 4runner V8 with 24000 miles. (Canada- cold)

I use regular gas.
I filled up the gas tank and reset the average fuel consumption.
I drove 158 miles 70% highway @ 55MPH rest is city driving.
I did 8 long stops (overnights and 10 hours during the day) and 40 short ones stop signs ...
The average displayed consumption was 18.4 MPG
I filled the tank at the same pomp and it used 10.4 G which averages to 15.3MPG.

This looks like a quite bad mileage. Also, I am concerned about the variation between the displayed value (18.4) and the real one 15.3.
I have repeated the test again with similar results.

Can somebody clarify this for me?
I would be helpful to know how, what sensors are used to calculate the fuel consumption. Does it measure the fuel flow through the gas line, one cylinder, all cylinders?

Thank you,
Calin

 

[toybox]

There has been many long discussions about the discrepancy between actual mileage and that reported by the displayed mileage. You should search for further information. But to make a long story short no one has figured out how to make it accurate.

I just bought a 2004 Toyota 4runner V8 with 24000 miles. (Canada- cold)

I use regular gas.
I filled up the gas tank and reset the average fuel consumption.
I drove 158 miles 70% highway @ 55MPH rest is city driving.
I did 8 long stops (overnights and 10 hours during the day) and 40 short ones stop signs ...
The average displayed consumption was 18.4 MPG
I filled the tank at the same pomp and it used 10.4 G which averages to 15.3MPG.

This looks like a quite bad mileage. Also, I am concerned about the variation between the displayed value (18.4) and the real one 15.3.
I have repeated the test again with similar results.

Can somebody clarify this for me?
I would be helpful to know how, what sensors are used to calculate the fuel consumption. Does it measure the fuel flow through the gas line, one cylinder, all cylinders?

Thank you,
Calin

 

[calin]

Thank you. If done some research and indeed I have foud peoples reporting discrepancy between the actual mileage and the displayed mileage.

One major issue I have is that if the error is so large 3.1MPG on my 4runner I might have a mechanical problem. It seems that the displayed value is computer estimated based on injector control, air flow, ... My worry is that I do not know the history of the car as I bougth it used.

 

[SidVicious]

Thank you. If done some research and indeed I have foud peoples reporting discrepancy between the actual mileage and the displayed mileage.

One major issue I have is that if the error is so large 3.1MPG on my 4runner I might have a mechanical problem. It seems that the displayed value is computer estimated based on injector control, air flow, ... My worry is that I do not know the history of the car as I bougth it used.

I am driving a brand new 07 T4R and I there is a discrepancy between the actual and displayed MPG. I've only filled up twice so far and these are my results:

First fill-up:
Actual - 16.2mpg
Displayed - ~16.6mpg (I don't remember exactly cause I didn't write it down.)

Second fill-up:
Actual - 15.3mpg
Displayed - 16.7mpg (I wrote this one down. : )

I have been driving like a grandma so far, since I have less than 700 miles on the clock. I am very interested how these numbers will change when I really put my foot into it.

I will keep an eye out and report back as things unfold.

 

[keylay31]

Guys. You say that you're driving like a grandma, but I'm getting ~20 mpg (21mpg displayed) (20.3 calculated). Granted, I have a v6... but still...

 

[SidVicious]

Guys. You say that you're driving like a grandma, but I'm getting ~20 mpg (21mpg displayed) (20.3 calculated). Granted, I have a v6... but still...

I have a V6 too. I would be very happy with your MPG numbers.

I am hoping that my MPG increases as the engine gets broken in. I have read on this forum about how some owners have experienced bad gas mileage during break in, and had increases thereafter. We shall see.

And not to take this thread in a totally different direction... I have used 89 octane in both fill-ups. Maybe 87 would yeild better MPG numbers.

 

[Kmvreter]

I gave up on the fuel economy display. It was anywhere from -30% to +10% off depending on the variation in going from a tank of city driving to another tank of highway miles.
I leave it set to "range". Combined with my trip odo and the idiot light, I judge when to fill up next.

 

[keylay31]

I have used 89 octane in both fill-ups. Maybe 87 would yeild better MPG numbers.

I use 85... =O, I've had mine for... 2 months.

and to address the original question, i don't rely on my in-dash display except to (lyingly) show off how good MPG my car gets (because my actual is normally lower than what the display says)

 

[toto]

It seems that the displayed value is computer estimated based on injector control, air flow, ...

You would think the trip computer has access to that data, but either it doesn't, or it just doesn't use it.

I think it's reading fuel consumption from the gas gauge, which is stupid because the gas gauge doesn't move off of "Full" right away even though you're driving. That's the only explanation I've been able to find for why it's coming up with an MPG that's better than it really is.

Just ignore the trip computer. Use it to display the outside temperature.

 

[dwm2112]

The sad part of this whole story is that Toyota makes some very solid vehicles but can't get the electronics to produce and accurate MPG figure. Even GM can manage that feat so it is puzzling that Toyota can't. I have the V8 and my display typically overstates the actualy by 1.5 to 2.5 MPG.

 

[calin]

I use 85... =O, I've had mine for... 2 months.

and to address the original question, i don't rely on my in-dash display except to (lyingly) show off how good MPG my car gets (because my actual is normally lower than what the display says)

Till I have figured up the real fuel consumption I have also made few gelous peoles with the displayed information.

 

[tedcool]

Short term average?

Hi All,
I wonder if the fuel economy display is showing a short(er) term average of the fuel economy. Not averaged since the 'reset'. It makes at least some sense... Maybe if you filled up at a highway fuel stop, hit reset, and then took a long highway trip at a relatively steady speed over one of the flatter states, then compared actual to displayed MPG at a fill up at another highway fuel stop, it might be close ( I hope!).

It would be very interesting if someone gets a chance to do this!

 

[calin]

Re: Short term average?

Hi All,
I wonder if the fuel economy display is showing a short(er) term average of the fuel economy. Not averaged since the 'reset'. It makes at least some sense... Maybe if you filled up at a highway fuel stop, hit reset, and then took a long highway trip at a relatively steady speed over one of the flatter states, then compared actual to displayed MPG at a fill up at another highway fuel stop, it might be close ( I hope!).

It would be very interesting if someone gets a chance to do this!

tedcool,
What I have is not exactly what you asked but during my test the average displayed values between 18.1 and 18.8 MPG. The actual is 15.3 far away from 18.4MPG displayed at the end of the test. If the average is a short term average (which I beleave it is) I should have had values < 12MPG at times in order to have the overall real average at 15.3 (at pump).

My understanding of the manual is that the average is the average since the last reset. What makes me beleave it is not the case is the variation of the average during my trips to work.
After a reset, day one, 2 3 4 all started at home at 18.8 goes quickly at 18.1 and slowly reach 18.8 when I arrive at work. A real average will change lesser as it accumulates data.

 

[tedcool]

I agree

I agree with you - my idea doesn't explain it very well either. Maybe a Toyota Tech Rep can shed some light on it...

 

[keylay31]

Re: I agree

I agree with you - my idea doesn't explain it very well either. Maybe a Toyota Tech Rep can shed some light on it...

maybe they can explain why such a tech-forward vehicle made by a company which such a high reputation for reliability has included such unreliable (and obviously unreliable) component in their SUV flagship.

 

[Falls]

Mine is pretty much right on ( give or take a little) from day 1 .

Seems I get the same milage no matter how I drive.

There are so many threads like this I can't explain it anymore.

 

[smokingun]

During break in and driving like a grandma's grandma, I got 21.1-22 MPG (gauge) and would play with driving at speeds to get it even higher.

Now that break in is over, I get around 19.9 gauge in routine driving. I haven't checked the math on an actual fill up. I'll report back!

Oh, this is on a v-8 LE.