Wow, most of your difference is 0.8 mpg or less! (only once was it around 1.9 mpg).

I think my first two tanks were within that range...it's just this third one.

When you say "...stoping at the second automatic shutoff", do you mean after the first time the pump stops, you "top off" by continuing to gas up until the 2nd time the pump stops? Do you actually get that much more on the 2nd pump action? I never really notice, but seems like whenever I tried to top off, I just get a second or two of gas, which didnt seem a lot to me so I've never top off anymore.

 

I generally run my cars to between 25 and 0 MTE on the gauge. When I fill up I slow the pump down at around 12.0 gallons or so. After the first time it shuts off, I wait a few seconds, top it off until it stops again and that is it. I used to go longer but it tended to overflow. Most of the time it is only a couple tenths between the first stop and the second but I do it that way to make sure the pump didn't just stop due to pressure in the tank.

 

Hi Ray

Thanks very much for digging out that information. For some reason the '05 calculation is off an average of 3.7MPG from the gauge over 7 tanks. Your '06 is only off an average of .6MPG calculation from the gauge over 7 tanks.

My guess is that you are as consistant as possible at filling your tanks and are not going into filling the air pocket very much. However, it does appear when you got the 1.9mpg worst than the gauge reading in your '05 fillup, you did. This is evident with the next plus .8 calculation reading over the gauge.

It is my opinion that the calculated mileage over those types of tank examples will become further apart from the gauge readings due to tire wear (mileage). A .6MPG difference with 9,500 miles on the tires is a reasonable explanation for your '06 gauge reading. Just one fillup into the air pocket of the '05 can make a big mess up in your 7 tanks of fillups. This has no bearing on driving shorter or longer distances and certainly does not suggest you incorrectly filled your tank!

GaryG

 

That's why I don't worry too much about individual tanks - variation in what a "full" tank really is. Long term it balances out. The tank milages in my spreadsheet look like an ekg but the lifetime average stays pretty steady. I'll try to get it posted somehow....

I haven't updated my database on here in quite a while. I have around 13,000 on the '06 and over 15k on the '05. If you look at the numbers I posted in the other post you can pretty easily see the point where my wife and I switched cars. Here local driving kills the average but she is getting better. This tank I am on now is running at almost 40 on the gauge with 250 miles and 280 MTE showing. The weather has cooled some so the a/c hasn't had to work I guess.

 

Hopefully, everyone that read this thread can use the good records you kept to better understand how to determine MPG. Thanks for letting us know the change in mileage from your date base, that increase in mileage makes more sense regarding tire wear.

Untill you have a gauge like the SG, its hard to determine what techniques work to improve your MPG. The fact is, if you use a combination of the fuel gauge, Nav or message center, and the SG, you know what your MPG average is throughout a single tank. The moment I pull into the gas station, I know what my average is and how much fuel remains in the tank before I add a single drop of fuel. Now that I've ran out of gas in my FEH, I know how much fuel I have left after 0 MTE based on my MPG average and miles traveled after 0 MTE. This is how I came up with the 1.3 gallons. If you read the comments from those who have the SG, they can't do without it for just a short time while it's being repaired or replaced. I feel the same way.

GaryG

 

LOL, how true. We are doing a replacement exchange for my SG II as we speak, I am keeping the defective one(It still works most of the time) until the new one arrives....

~John

 

Mine is usually very close to the calculations, and I've had 2 where the calculations are higher than the Nav displays.

 

The last 2 tanks I checked both came out the under 29 mpg (28.5 and 28.1 mpg), even though my 15 minute average mpg stayed above 29mpg and seemed to spend the majority of the tank above 30mpg.

I have ~1500 miles on my 2007 FEH.

 

This probably isn't the right thread for this one, but I have noticed that the NAV display, the SG, and the actual pump readings all differ by 1 or 2 MPG. C'est la vie.

But my real reason for posting is that long ago, in another life, there was some debate about the meaning of the "average" MPG that the NAV display shows. It was alleged by someone (I don't recall who) that it was an average over 2000 readings of something or other.

Anyway I pestered Ford about this for a long time (the trigger was that someone tried "whassamatta, don't you understand the word average?"), and Ford now officially tells me the following: there are two accumulators that collect gas and mileage as they are used (Ford didn't deign to tell me in what units they are collected), and the totals are divided, to produce the display. That's legit. Both accumulators can read only to 1000 (that's why the units matter), and when either one reaches 1000 they both switch to a rolling window, discarding old data points as they add new ones.

If I understand this correctly, it will always be the mileage accumulator that hits 1000 first, even if the fuel accumulator reads tenths of a gallon. Assuming (since they didn't tell me) that the mileage accumulator really accumulates miles, and the fuel accumulator tenths of gallons, that would mean that (absent a manual reset) the mileage accumulator would always be near 1000, and the fuel accumulator always near 30 gallons, displaying the quotient on the NAV unit.

This could be tested. For an average driver, getting around 30 MPG, one has to find a long downhill stretch that uses no fuel, in which case the "average" display on the nav should increase 0.1 MPG every three miles. That assumes that the mileage accumulator measures in miles, something Ford didn't actually say. The fuel accumulator shouldn't change while this is going on, since no fuel is being used.

I'll bug Ford about the accumulator units.

Cheers,
Hal

 

I have wondered about this since I bought the car. Your information makes the whole thing make more sense.

I would assume (guess) that the accumulator for mileage is just an encoder that counts revolutions of one of the wheels or output shafts since anything in the transmission or engine can vary in ratio. From there I would guess that the computer converts revs to distance.

As for the fuel flow, whatever units they measure in, I would guess that is probably where the error comes from. Variations in temperature and even a very minor error in calibration could account for a mile or two per gallon error, easily.

Having a moving window of 1000 data points is probably as many as can realistically be expected to maintain some semblance of accuracy.

Just a wild-assed guess this early in the morning though.

How are you enjoying the FEH Hal?