Fuel mileage estimation problem

[Elan750]

Before I begin, I am aware that I wouldnt have the problem if I filled up more often. Thanks mom and dad. But this is something that just developed and Its driving me nuts.

Going back about a month or so ago. I drive about 60 miles a day, mostly highway. On the way to work I was getting low on gas, very low. I rolled into the gas station with only 1 mile left on the screen that tell s me how much further i can go. I often would see it go down to about 10 miles, but it was somewhat pleasing to see it go to 1 and not run out of gas. :happy:

a week later, i run out of gas. The meter said I had 18 miles left. So im thinking that going down to 1 might have messed something up? I decided that I should stay above 25miles to be safe.

This morning I ran out of gas again. The meter said I had 28 miles left. The gas light on the dash didn't go on, and the needle said I had about 1/8th tank.
A few other notes, When I added the 1gallon jug of gas, the meter doesnt notice. Does it just reset with a full tank? or could it now be a gallon off judgement?

When I filled up the tank, the meter estimated 355 miles. I calculated with my mpg and the 23 or so gallons x 17mpg(being generous), and I got 390 miles. so this completely contradicts what it has been telling me previously.

Any ideas?

 

[ray k]

I don't think 1 gallon would read on the gauge. I've put in 2-3 gallons before and the needle didn't move. Not to preach...but I've heard not to let it get below 1/4 because it's bad for the fuel pump.

 

[Montego Murph]

I'm not exactly sure on the process (maybe just disconnecting the battery and holding the brake for 30 seconds) but maybe the system needs a little reset & recalibration.

Do you top off the tank each time or simply add 10 gallons here or there? The way liquid sloshes around in the tank as you drive and driving/parking surfaces are not always perfectly level, it would be difficult for the fuel gauge to measure accuracy beyond maybe a half gallon. Otherwise it's all about averages, estimations, and optimism. My theory is that since the Fuel-puter in the dash is only vaguely accurate to begin with, the only thing that would really provide a rock solid measurement is filling the tank to the top and the fuel level sensor reads "filled to the top." Consider the following:

• The MPG computer (for whatever reason) tends to read 10-15% optimistic by design.
• The Fuel Level is reporting an average of readings as fuel splashes around in the tank. (Visualize trying to measure the height of a packing peanut floating in a pot of water in a moving vehicle.)
• I have heard, and it seems plausible, that the "Range" is purposely programmed to be a few miles pessimistic to make sure if it's wrong, it leaves the driver with excess fuel instead of not enough.
• The Fuel Range display is calculated from those three figures stated above. "Seems like there's about 12 gallons in there, and he's getting 22mpg, plus these other arbitrary numbers...."

TL;DR:
If you don't fill your gas tank to the top every so often, the LCD display might be showing you bad info.

 

[Elan750]

I'm not exactly sure on the process (maybe just disconnecting the battery and holding the brake for 30 seconds) but maybe the system needs a little reset & recalibration.

Do you top off the tank each time or simply add 10 gallons here or there? The way liquid sloshes around in the tank as you drive and driving/parking surfaces are not always perfectly level, it would be difficult for the fuel gauge to measure accuracy beyond maybe a half gallon. Otherwise it's all about averages, estimations, and optimism. My theory is that since the Fuel-puter in the dash is only vaguely accurate to begin with, the only thing that would really provide a rock solid measurement is filling the tank to the top and the fuel level sensor reads "filled to the top." Consider the following:

• The MPG computer (for whatever reason) tends to read 10-15% optimistic by design.
• The Fuel Level is reporting an average of readings as fuel splashes around in the tank. (Visualize trying to measure the height of a packing peanut floating in a pot of water in a moving vehicle.)
• I have heard, and it seems plausible, that the "Range" is purposely programmed to be a few miles pessimistic to make sure if it's wrong, it leaves the driver with excess fuel instead of not enough.
• The Fuel Range display is calculated from those three figures stated above. "Seems like there's about 12 gallons in there, and he's getting 22mpg, plus these other arbitrary numbers...."

TL;DR:
If you don't fill your gas tank to the top every so often, the LCD display might be showing you bad info.

I do fill it up to the top every time. (crazy not to!) I think the range is calculated based on your current MPG, not programmed, but i'm not sure. Mine seems to be getting more and more optimistic.

The thing is that the display is saying 27miles left, AND according the the physical needle on the dash, I have more gas to go as well. This is telling me there may be a fuel pickup issue.

I just struggle to just settle and keep it above 1/4 tank. I've never had this problem since i've owned the vehicle, and with my high mileage, i'd have to get gas 3-4 times a week.

 

[Montego Murph]

I do fill it up to the top every time. (crazy not to!)

My bad... I read "...if I filled up more often..." as "I never top it off, just throw a few bucks in every few days.

(I swear I'm going to pull an eye muscle if I have to hear another friend or co-worker explain to me that they're saving money by putting $10 in every few days instead of filling their tank all the way when needed.)

 

[ray k]

My bad... I read "...if I filled up more often..." as "I never top it off, just throw a few bucks in every few days.

(I swear I'm going to pull an eye muscle if I have to hear another friend or co-worker explain to me that they're saving money by putting $10 in every few days instead of filling their tank all the way when needed.)

What's their logic on only partially filling up saving them money?

 

[Montego Murph]

What's their logic on only partially filling up saving them money?

I'm going to blame it on being very good at math, but very bad at logic.

Somehow they feel that by spending less money at each transaction, that money is being saved. "Well duh, if I spent $45 instead of 10, how is that saving money?" In and of itself, this is a true statement. 10 is mathematically less than 45.

However they refuse to believe that:
1) Their fuel consumption is going to stay the same regardless of when it is purchased,
2) They are actually using MORE gas (and time, assuming their time has value) diverting from their route to add a little fuel every day,
3) They could save money by topping off when prices drop a few cents instead of buying a few gallons daily regardless of price.

Now granted, in fuel savings we're talking about cupfuls and dimes, not any life-altering quantity...

Of course, one of these is the same friend who got into a pissing match with me insisting that her Escalade got better gas mileage than my Miata, because the Caddy could go 540 miles on a tank, whereas my Miata could only go 392 miles. :shocked:

 

[ray k]

I'm going to blame it on being very good at math, but very bad at logic.

Somehow they feel that by spending less money at each transaction, that money is being saved. "Well duh, if I spent $45 instead of 10, how is that saving money?" In and of itself, this is a true statement. 10 is mathematically less than 45.

However they refuse to believe that:
1) Their fuel consumption is going to stay the same regardless of when it is purchased,
2) They are actually using MORE gas (and time, assuming their time has value) diverting from their route to add a little fuel every day,
3) They could save money by topping off when prices drop a few cents instead of buying a few gallons daily regardless of price.

Now granted, in fuel savings we're talking about cupfuls and dimes, not any life-altering quantity...

Of course, one of these is the same friend who got into a pissing match with me insisting that her Escalade got better gas mileage than my Miata, because the Caddy could go 540 miles on a tank, whereas my Miata could only go 392 miles. :shocked:

How could you not laugh in her face about the 6000 lb, V8 escalade vs the 2500 lb miata? [emoji23] Did you explain how her gas tank is twice the size as yours?