Fix for the lying on board MPG readout?
08-24-2016, 06:31 PM
#51
You make a big assumption. Not everyone top off their tanks until fuel is pouring out. As a personal example, I round to the nearest multiple of .05.. My readout is within 5% actual (or a close as I can figure without using a lab flowmeter) and that the odometer is accurate. One of these days, I'm going to test it against a full tank of non-oxy fuel. I'm willing to bet it will be very close to on the money.
Sorry to offend you!
08-24-2016, 09:05 PM
#52
I logged 11 consecutive tanks, 316 gallons. The lie-o-meter was within +/- 1% of itself for nine tanks and +/- 2% for the other two. That's plenty precise.
The problem is that Ford set the zero point wrong and that excellent precision is bouncing around a 7% error from the correct figure.
I don't have any interest in MPG but I'd like to know at a glance exactly how much gas I've got left and between the miniature analog gage on my XLT and the trip computer lying by upwards of 2 gallons by the end of the tank I have to stop and think about it.
The problem is that Ford set the zero point wrong and that excellent precision is bouncing around a 7% error from the correct figure.
I don't have any interest in MPG but I'd like to know at a glance exactly how much gas I've got left and between the miniature analog gage on my XLT and the trip computer lying by upwards of 2 gallons by the end of the tank I have to stop and think about it.
Last edited by aspade; 08-24-2016 at 09:08 PM.
08-25-2016, 07:24 AM
#53
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I'm not offended. But just because you or I do something, it doesn't mean several hundred thousand others do the same thing. I just think you are drawing conclusions from your own experience and those who echo the same thing. It doesn't mean it's correct, nor does it mean it's incorrect.
Just remember the first three and last two letters of assume. And no offense meant.
08-25-2016, 09:06 AM
#54
Senior Member
08-25-2016, 03:46 PM
#56
My XLT is about 5 weeks old. 4 tanks thru it so far. Analog gas guage is so far off as to be useless. Never reads over 3/4s, drops to 1/2 with in 50 miles of a fill. I depend on the computer to keep me apprised of the fuel state. Seems accurate enough. At least I haven't run out of gas yet. 
Each fill has taken around 24 gallons +/- 2 to activate the nozzle shut off. Seemed reasonable to me as I waited for the computer to warn me of low fuel, which I suspect cuts in when it feels you are down to 50 miles range. Since the computer thinks Im getting 21 in the city and 25 hwy, that all jives.
But today I had occasion to look at my window sticker (no, not on the truck anymore) and find that although I did not want or need or request it, my truck came with and I was charged $400 (sticker) for a 36g tank!! So did I get taken by the dealer, or is the computer so far off that it is not calculating for the big tank and I really have 8-10 gallons left when it's warning me of low fuel? Or is there a hidden saddle tank I have to switch to?
Each fill has taken around 24 gallons +/- 2 to activate the nozzle shut off. Seemed reasonable to me as I waited for the computer to warn me of low fuel, which I suspect cuts in when it feels you are down to 50 miles range. Since the computer thinks Im getting 21 in the city and 25 hwy, that all jives.
But today I had occasion to look at my window sticker (no, not on the truck anymore) and find that although I did not want or need or request it, my truck came with and I was charged $400 (sticker) for a 36g tank!! So did I get taken by the dealer, or is the computer so far off that it is not calculating for the big tank and I really have 8-10 gallons left when it's warning me of low fuel? Or is there a hidden saddle tank I have to switch to?
08-25-2016, 04:54 PM
#57
Elmote, sounds like you need to have the dealer check yours out. One time I had the
fuel light come on and it took a little over 30 gals to fill up. Even when it get's low without
the fuel light it will still be close to 30 gals.
Also, I hand checked mine the other day, it was showing 17.2 but actually was 16.0.
fuel light come on and it took a little over 30 gals to fill up. Even when it get's low without
the fuel light it will still be close to 30 gals.
Also, I hand checked mine the other day, it was showing 17.2 but actually was 16.0.
08-25-2016, 05:25 PM
#58
State testers measure by volume. But a gallon of fuel changes with temp. So in theory, you get more fuel when you fuel up at a station where the temps have be subzero for days and the fuel is colder. Colder fuel is 'denser' and contains more energy (BTU) than warm fuel in the summer. They take into account differences between summer and winter fuel mixes. Winter fuel has more volatile components so it is easier to start when cold, which negates the increased energy being denser when cold.
Then subtract idle times for either warming up (for you unfortunates who live in cold climates) or sitting with the AC running (for those of us who are unfortunate to live in the sweltering south and southwest). I read somewhere an hour of idle can burn over 2 gallons of fuel which you don't take into account when trying to figure actual MPG. The meter does show a drop in MPG as you idle.
Then subtract idle times for either warming up (for you unfortunates who live in cold climates) or sitting with the AC running (for those of us who are unfortunate to live in the sweltering south and southwest). I read somewhere an hour of idle can burn over 2 gallons of fuel which you don't take into account when trying to figure actual MPG. The meter does show a drop in MPG as you idle.
08-25-2016, 05:30 PM
#59
While I agree that you can't get exact numbers by hand calculating, you can certainly get averages. For example, in 54 fill-ups, my truck has calculated the fuel economy .621 mpg too optimistically. Only 2 out of 54 times has the truck been less optimistic than my hand calculations, and those outliers may be typos for all I know.
The trend I see is that with warmer weather makes the truck a bit more optimistic than cooler weather. I haven't noticed any other correlations on the data that I collect.
I don't trust GPS mileage. I've noticed that with Garmin Mechanic, it's off for shorter trips with more idle time. For example, I drive 100 miles and it seems to be dead on, but if I drive 3 miles to work from the gas station in stop and go traffic, it's often 4-5 mpg different than my truck readout.
What I do know, is that I've purchased what I'm told is 1,660.839 gallons, driven what the truck thinks is 31,537.4 miles, and that it costs me 13.87 cents per mile in fuel to drive this truck. (I burn premium, mostly, so that's probably a bit higher than most.) This is what I'll sell the truck based on, and I'll likely give the new owner the spreadsheet, so that he's aware of the truck's history.
Pic of my records:
The trend I see is that with warmer weather makes the truck a bit more optimistic than cooler weather. I haven't noticed any other correlations on the data that I collect.
I don't trust GPS mileage. I've noticed that with Garmin Mechanic, it's off for shorter trips with more idle time. For example, I drive 100 miles and it seems to be dead on, but if I drive 3 miles to work from the gas station in stop and go traffic, it's often 4-5 mpg different than my truck readout.
What I do know, is that I've purchased what I'm told is 1,660.839 gallons, driven what the truck thinks is 31,537.4 miles, and that it costs me 13.87 cents per mile in fuel to drive this truck. (I burn premium, mostly, so that's probably a bit higher than most.) This is what I'll sell the truck based on, and I'll likely give the new owner the spreadsheet, so that he's aware of the truck's history.
Pic of my records:
08-26-2016, 09:56 AM
#60
Can any one verify if there tank is filled to the same level each time they fill up? The pumps are checked by weights and measure to ensure gas stations aren't ripping you off. How ever, it's very easy to electronically cheat that system. The you have to consider that the pumps them selves are mechanical in how they determine full. No two are the same. Heck, even air temp will change when the things shut off. So, every time you fill your tank ends up at a different level.
Let's say you start with a tank at level A. You drive about (your odometer is off by a bit)
You then fill and the pump stops at level B. You don't really know the exact amount you used, only how much you put in.
Your hand calculation will be off but not by much. Maybe 5%
The built in MPG will also be off, which is accurate? Neither. There both off by a bit.
Manufactures could build a MPG readout that is exactly accurate but the cost would be astronicomal and then it would only be accurate until parts wear. It's why labs have to have there measuring equipment calibrated.
Let's say you start with a tank at level A. You drive about (your odometer is off by a bit)
You then fill and the pump stops at level B. You don't really know the exact amount you used, only how much you put in.
Your hand calculation will be off but not by much. Maybe 5%
The built in MPG will also be off, which is accurate? Neither. There both off by a bit.
Manufactures could build a MPG readout that is exactly accurate but the cost would be astronicomal and then it would only be accurate until parts wear. It's why labs have to have there measuring equipment calibrated.