As I said before, if the odometer if off, it is also off for the caclulation the computer makes. As for your other 1% or 2%, your assuming the computer is more accurate, I don't think that is a good assumption.

 

The computer uses an estimate algorithm with one variable, distance traveled. that may or may not use the odometer, but is still based on 1 variable and a constant math formula.

The manual method has 2 variables, the odometer and the pump.

If the odometer is off by +-1%, the computer will be off by +-1%, but should be consistent.

If the odometer is off by 1% then the manual method will vary by 0% to +-3% depending on the pump.

Human vs. computer error is a whole other issue, but these are not complicated calculations for either.

 

Ian's logic is correct IMO. If your display reads 40mpg for a tank, then reads 38mpg the next tank, you somehow lost 2mpg. It really doesn't matter if the figures are spot on, what matters is the difference is spot on. And I agree that there would be no better method to measure that difference.

I use the on board display to achieve the best mileage I can (relative to itself). The important thing is the trends. I dabble in weather instruments and we run into the same problem. My barometer may not read the same as the next guys, but it's the trends that matter.

 

Ian33: The computer uses an estimate algorithm with one variable, distance traveled. that may or may not use the odometer, but is still based on 1 variable and a constant math formula.

There has to be at least one other variable, probably rate of fuel flow, or all it could tell you is distance. btw: if you don't think it's using the odometer for distance, what do you think it is using?

My point is simply that the MPG computer is not a highly tuned machine and I don't think you should expect it to be more accurate than distance/fuel. It is however likely to be more consistent.


steved28: My barometer may not read the same as the next guys, but it's the trends that matter.

yes, you want to look at your trend and if your not driving differently but notice a change in mileage, you want to figure out why.

 

The computer readout for MPG is based on 1) the milage traveled as measured from the same sensor used for the odometer, and 2) the fuel used, which I believe is a count of fuel injector injection droplet pulses. The fuel consumption has the highest probability of error as many factors can cause it to vary (temperature, fuel pump pressure, injector cleanliness, etc.). It is probable that Toyota compensates for many of these factors, but that only reduces, not eliminates, the compensated source of error. Most compensation requires a separate sensor, such as a thermometer, which will also have some error. Very few sensors on the car will be as precise as the odometer, except for time based measurements. Time is measured with great accuracy and precision.

-- Alan

 

See my story in Roll call... how many Altima hybrid owners are here? I have several times put in almost 20 and 2 times at different stations 22 gallons.
Bruce

 

I filled my NAH at another gas station today. I purposely drove the car with "0 miles to empy" showing on the display for 22 miles and the needle just above the "Empty" line on the gauge. When I pulled into the gas station, I was guessing that I'd have about 2 gallons (or slightly less) in the tank. When I filled the tank, I put in 18.09 gallons. This sounds right to me as the NAH holds 20 gallons.

Recall that, at the same point, the gas station near my house claimed that I filled the tank with 19.9 gallons. Impossible. I decided to double-check this evening by filling my scooter at that gas station. The scooter holds 1.2 gallons, but I have never filled over 1 gallon when the gas gauge points to the bottom of the red area ("Very Empty") That gas station told me that I filled 1.12 gallons into the tank. May not sound like a big difference, but that .12 gallon difference makes up the roughly 2 gallon difference on a 20 gallon fill.

So I have convinced (if only myself) not to use that gas station anymore.

 

You can help other people, if you will report that station to the authorities.
It will only take a few minutes of your time, and it will save a lot of other people a lot of money.

All you have to do is fill out a form and send it to the county by fax or snail-mail. The county will send an inspector to check the pumps at that station. It is possible, though unlikely, that the station owner does not know that his pumps are not properly calibrated. The form, fax#, and snail-mail address are available online at: http://www.ocagcomm.com/wm_complaints.asp

 

It is important to report these stations to the proper authorities. It's obviously an issue and probably much more prevalent than most care to acknowledge. It's always easier to wait for the next person to take the initiative because we're always too busy, but sometimes you just need to take 5 minutes and do something. It'll make you feel good if nothing else...

 

If you are so concern at being ripped off, just document it yourself. Get a 5 gallan plastic tank and fill to the 5 gallon mark. Check the readout. If it is off, then complain.