Gas Mileage Problems?

[Macaque]

Searched but I couldn't find anything pertaining to my specific issue.

I drive a 2009 SE with the V6. Every time I fill up my tank I reset my odometer/trip computer and reset my gas mileage calculator (the one on the AC display). I fill up my tank at the same gas station and in the same way every time. I let the pump go until it clicks off and I don't top off.

Say I drive 280 miles and have 1/4 of a tank left when I fill up. My gas mileage gauge will tell me I'm getting 20.4 mpg. Going off of that, I should take in 13.7 gallons. When I actually fill up, however, I'll take between 15 and 16 gallons, meaning that my gas mileage was significantly lower than what my gauge is telling me. I don't like this discrepancy. Anyone else have the same issue and know why it happens?

 

[BlackWorksInc]

There are a number of threads that have popped up, including a few posts I wrote that tried to analyze and explain how the fuel mileage computer calculates fuel mileage. Unfortunetly no one has really be able to accurately predict how the system works (I came close, but the numbers were always off by some small unpredictable amount from a variable the system uses I cannot guess what. Toyota doesn't explain how the system actually functions more than a description in owner's manual.)

The trend is that these fuel mileage monitors are always more optimistic than what you are actually getting and there is no real way to correct the discrepency as far as I know. It seems to always be 10~15% over what you are really getting.

 

[03_4x4Runner]

Just put a piece of tape over the mpg part of the display and forget it. They are not accurate at all.

 

[Texas_4Runner]

The only way to get a proper MPG calculation is to fill up. Reset the trip odometer. Drive. Fill up.

Miles driven divided by gallons needed to fill up. Repeat that every time you fill up and get an average.

 

[Macaque]

That's what I've been doing. You'd think they'd have figured out how to make an accurate MPG meter by now haha.

 

[03_4x4Runner]

My 2011 Avalon is the same way, always 2 mpg optimistic.

 

[JDSupreme]

I leave mine in "blank mode". It drove me nuts looking at the MPG and range.

Do the math :whip2:

I get around 16 hilly short distance city driving with a mix of towing 1700lbs in there

 

[boondoggle]

What JD said. It'll drive you crazy to think about it.

I haven't covered mine only because I can show it to my wife and she'll think I'm really getting 18/19mpg.

I prefer just setting it to Range. It's like a digital fuel gauge that way.

 

[Martinjmpr]

I have a Scangauge II that does many of the same functions, the major difference being that unlike the factory gauge, I can calibrate my Scangauge.

Yes, it is consistently 2mpg optimistic. What's funny is that the "range" display must include a healthy reserve because that is almost always less than what my Scangauge shows.

IOW, when the factory gauge shows 21 MPG and 400 miles range (on a full tank) my SG will show a more realistic 18 MPG but 415 miles range.

Not only that, but as I drive, the "range" drops on the factory gauge much faster than on the scangauge. At around 1/4 tank, my SG will show me still having 95 miles to empty while the factory gauge shows my range as under 50.

 

[MikeInNH]

Mine is all over the map. Sometimes it's close..other times it's more then 6mpg off. It's NOT accurate. And from everything I've read no manufacturer has an accurate one. The algorithm used to figure out mileage just can't account for all the different variables.

The best way is to take the number of miles driven since your last fillup and divide by the number of gallons you added. Take the average over several tank fillups to get a more precise.

 

[M1911]

The computer on my '03 V8 is always 1-2 mpg optimistic. It's been that way since it was new.

 

[Martinjmpr]

And from everything I've read no manufacturer has an accurate one. The algorithm used to figure out mileage just can't account for all the different variables.

I've noticed the same thing on my wife's Grand Vitara. IMO the biggest problem is the inability to calibrate. Seems to me if they're going to go to the trouble of putting a gauge like that on a vehicle, they should give you a way to calibrate it.

I've used both a Scangauge II and an Ultra-Gauge and both are easy to calibrate (the Scangauge is easier but the Ultra-Gauge allows a finer calibration.) Once calibrated both are amazingly accurate.

In fact, on a recent trip to Oregon, I had the SGII on my 3rd gen (99) 4runner and it accurately predicted exactly when I would run out of gas 6 miles outside of Prineville. I hit "0" miles Distance to Empty and about 5 miles after that, I actually ran out of gas.

 

[Javelin]

I calculated mine today. (275.7 miles ÷ 19.6 gal)

Comes to 14.0 exactly. My readout says 14.6.

So ya.....its off

 

[radlynx]

i just filled up today and i got around 17.58 MPG. i used to get around 20mpg when it was new. i am not at 80 miles and i'm planning on changing my oxygen sensor but having a hardtime replaceing it. it's too tight in there. hopefully it helps with my mpg. what's you current mileage?

I calculated mine today. (275.7 miles ÷ 19.6 gal)

Comes to 14.0 exactly. My readout says 14.6.

So ya.....its off

 

[ChaosStarter]

i just filled up today and i got around 17.58 MPG. i used to get around 20mpg when it was new. i am not at 80 miles and i'm planning on changing my oxygen sensor but having a hardtime replaceing it. it's too tight in there. hopefully it helps with my mpg. what's you current mileage?

For the record, you have 4 total oxygen sensors actually. The top two (closer to the engine) on each side would be the ones you want to change since those read the Air/Fuel ratio.... So you need to change 2.