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Actual fuel tank size?

33K views 37 replies 26 participants last post by  rollinhonda 
#1 · (Edited)
With so many discussions on mileage and not having an on board computer to calculate it, I'm curious. How do you know how much you've used? The gauge isn't broken down into gallons or anything, and even if you tried to fill up on one of the hash marks, chances are you're still going to be +/- some amount. If I'd paid more attention in math class, I could probably figure out the margin of error in mpg if you're off by even a half gallon.

And I know that the manual says 22.00 gallons, but today I filled up after cruising around with the low fuel light on for a few days. It was below the bottom hash mark, and I only put 17.9 in it? And that's the most I've ever been able to get in-Normally if I fill up soon after the light goes on, I'm putting in 16-17 gallons. Surely there isn't a 5-6 gallon reserve? I do miss the 'Distance to Empty' calculator on my MB-was fun to pull into a gas station with it reading '3'.:)
 
#2 · (Edited)
scottIN said:
With so many discussions on mileage and not having an on board computer to calculate it, I'm curious. How do you know how much you've used? The gauge isn't broken down into gallons or anything, and even if you tried to fill up on one of the hash marks, chances are you're still going to be +/- some amount. If I'[d paid more attention in match class, I could probably figure out the margin of error in mpg if you're off by even a half gallon.

And I know that the manual says 22.00 gallons, but today I filled up after cruising around with the low fuel light on for a few days. It was below the bottom hash mark, and I only put 17.9 in it? And that's the most I've ever been able to get in-Normally if I fill up soon after the light goes on, I'm putting in 16-17 gallons. Surely there isn't a 5-6 gallon reserve? I do miss the 'Distance to Empty' calculator on my MB-was fun to pull into a gas station with it reading '3'.:)
This is truly a new one on me. You must have gotten the optional fuel tank. The 18.5 gal tank option is not a very popular option though. Hmmmm.

ok, all kidding aside. the tank cap is 22.1 gallons.
to determine the mpg:
1. fill up tank. when you get your first nozzle auto shut off. stop. do not top off.
2. when you get back in your truck, reset the odometer (trip a or trip b).
3. drive around till your next refill. fill up tank as in #1 above.
4. make note of the miles on the odometer. divide this number by the amount of gas you put in your tank. = mpg
 
#3 ·
Could it be that your regular gas station is on a hill? this can impact your fill. How quickly does it go from full to a little below the full line? If it is pretty fast then it is likely you aren't getting a complete fill. The low light comes on with about 3 to 4 gallons left I believe (although I think the manual says 2 gallons).
 
#5 ·
Hi ScottIN,

Have you ever calculated you MPG? I wonder if your getting some crazy amount like 25MPG?

I wonder if the gas pumps are off a bit?

Maybe the pumps show 17 gallons but you are really putting in 19-20 gallons which would show in your MPG. Let us know.
 
#6 ·
ninefive0 said:
Hi ScottIN,

Have you ever calculated you MPG? I wonder if your getting some crazy amount like 25MPG?

I wonder if the gas pumps are off a bit?

Maybe the pumps show 17 gallons but you are really putting in 19-20 gallons which would show in your MPG. Let us know.
Point me toward those pumps that give you more than you pay for.:p
 
#9 ·
I can say that I have driven my truck 323.3 miles before I refilled but I am guilty of topping off. I have added as much as 20.0 gallons back into the tank.
 
#10 ·
Hey, you guys better be careful! Ya know, Inspector Honda doesn't want us to know what fuel economy we're getting. Remember, they took away our trip computer functions for a reason. If you guys go and tell everybody the secret formula for figuring out how to calculate our own gas milage, he's gonna' be mad! He said that we wouldn't understand what the numbers meant and that we would be confused. Oh boy, Oh boy! I think ya let the cat out of the bag now! Somebody's gonna' be in trouble....
 
#11 ·
Not topping off runs the risk that the pump you are using has a differently calibrated nozzle to shut off earlier or later than the previous nozzle you used. At least with the top off, you can see the gas at the top level. After your experiment is over to test fuel mileage you can stop topping off as someone mentioned somewhere else that the topped off fuel is wasted somehow on this truck (although I don't understand how that is happening):confused:
 
#12 ·
Ultra-HOG said:
Hey, you guys better be careful! Ya know, Inspector Honda doesn't want us to know what fuel economy we're getting. Remember, they took away our trip computer functions for a reason. If you guys go and tell everybody the secret formula for figuring out how to calculate our own gas milage, he's gonna' be mad! He said that we wouldn't understand what the numbers meant and that we would be confused. Oh boy, Oh boy! I think ya let the cat out of the bag now! Somebody's gonna' be in trouble....
Indeed, I'll forever curse Honda top management for this. It's just a plain ass boneheaded idea to remove the feature because they are afraid of a bad JD Power survey brought down by a few people reporting bad MPG. Education is the key not taking away features, sheesh. Just about every modern auto has a trip computer now, do they really think we don't know about it and won't miss it. I hope it really bites them in the ass and someday they'll re-enable it. All it takes is some top exec to give the go ahead and they can release a new NAV DVD with firmware to unlock it, that simple.
 
#13 ·
I think there is some variance as to when the light comes on. The few times I have let it get that low, it has taken about 20 gal., so only 2 gal. left. Looks like the range is 2-4 gallons for light on.
 
#14 ·
BillB said:
Not topping off runs the risk that the pump you are using has a differently calibrated nozzle to shut off earlier or later than the previous nozzle you used. At least with the top off, you can see the gas at the top level. After your experiment is over to test fuel mileage you can stop topping off as someone mentioned somewhere else that the topped off fuel is wasted somehow on this truck (although I don't understand how that is happening):confused:
Not all fuel in a topoff situation necessarily stays in the tank. Topping off you run the risk of gas overflowing into your vapor chamber. This is designed to reduce vaper emissions from your gas tank and protect the environment. By running liquid into your chamber you can foul it making it less effective if effective at all. This fuel does not then make it into your fuel lines to run the truck. So in general it is a good idea not to topoff, just fill until the click. If you track mileage from tank to tank and you worry about one tank you will forever be at a loss because you aren't considering the long term. Really gas mileage calculation over the life of your vehicle is far more interesting than each point in time. And the little difference in how full the tank was disappear.
 
#15 ·
If you slow the pump down (or stop it briefly) when you're a few gallons shy of being full, the vapors will have a chance to settle and won't prematurely trigger the auto-stop on the pump nozzle.

At least that's how I understand it. :)

And yeah, topping off is inadvisable for a number of reasons (read the manual! :D ).
 
#16 ·
Tex's Ridge said:
This is truly a new one on me. You must have gotten the optional fuel tank. The 18.5 gal tank option is not a very popular option though. Hmmmm.

ok, all kidding aside. the tank cap is 22.1 gallons.
to determine the mpg:
1. fill up tank. when you get your first nozzle auto shut off. stop. do not top off.
2. when you get back in your truck, reset the odometer (trip a or trip b).
3. drive around till your next refill. fill up tank as in #1 above.
4. make note of the miles on the odometer. divide this number by the amount of gas you put in your tank. = mpg
See, I never thought of using the tank at 'full' to calculate it-I was trying to work from the hash marks. And honestly, this is the first car I've had in close to 20 years that does not have a mpg function built in, so I've never thought about how to figure it.

Oh yeah-maybe I did get the optional smaller tank.:) Or Kroger's meters are off a bit:confused: AT $1.87 / gallon don't much care either way.
 
#17 ·
scottIN said:
See, I never thought of using the tank at 'full' to calculate it-I was trying to work from the hash marks. And honestly, this is the first car I've had in close to 20 years that does not have a mpg function built in, so I've never thought about how to figure it.

Oh yeah-maybe I did get the optional smaller tank.:) Or Kroger's meters are off a bit:confused: AT $1.87 / gallon don't much care either way.
BTW, someone made a comment that not topping off could cause incorrect readings. That could be possible, but topping off will not change that. Also, try to use the same gas station all the time. Of course this is not possible for travelers.
 
#18 ·
flymuck said:
If you slow the pump down (or stop it briefly) when you're a few gallons shy of being full, the vapors will have a chance to settle and won't prematurely trigger the auto-stop on the pump nozzle.

At least that's how I understand it. :)

And yeah, topping off is inadvisable for a number of reasons (read the manual! :D ).
Hey Fly, you said "premature":D
 
#19 ·
captmiddy said:
Not all fuel in a topoff situation necessarily stays in the tank. Topping off you run the risk of gas overflowing into your vapor chamber. This is designed to reduce vaper emissions from your gas tank and protect the environment. By running liquid into your chamber you can foul it making it less effective if effective at all. This fuel does not then make it into your fuel lines to run the truck. So in general it is a good idea not to topoff, just fill until the click. If you track mileage from tank to tank and you worry about one tank you will forever be at a loss because you aren't considering the long term. Really gas mileage calculation over the life of your vehicle is far more interesting than each point in time. And the little difference in how full the tank was disappear.
Yeah! What he said!!!:)
 
#21 ·
Ultra-HOG said:
Hey, you guys better be careful! Ya know, Inspector Honda doesn't want us to know what fuel economy we're getting. Remember, they took away our trip computer functions for a reason. If you guys go and tell everybody the secret formula for figuring out how to calculate our own gas milage, he's gonna' be mad! He said that we wouldn't understand what the numbers meant and that we would be confused. Oh boy, Oh boy! I think ya let the cat out of the bag now! Somebody's gonna' be in trouble....
The 2007 model has the Navi's Calculator function disabled and all places where a pencil and scrap of paper could be stored have been removed. Also, the trip meter zeros every time you kill the ignition and an optional blindfold is provided in case you accidentally read the gas pump display. Accidental filling with diesel is expected to rise.

[/sarcasm]
 
#23 ·
There are many factors that determine your individual miles per gallon. The ONLY thing we have in common is we have the same truck. Factors that are different but must be taken into consideration are: Driving Style, Geographic Location, Fill Up Habits, Tire Type and Pressure, Loaded Weight, etc. Now, for all of the above factors there are many factors that will cause your individual gas milage to vary, such as: Ambient Temp, Geography, Tire Pressure, City or Highway, Wind Load, etc.
Now with all of these above conditions it should be impossible to determine if your truck you drive in Texas gets better or worse gas milage than the one driven in Colorado or Ohio or California...right? In my truck, I have gotten between 14.7 and 23.3 mpg!!! Quite a range but considering what I was doing when I got the above figures I know they are correct. If you are really serious about checking your gas milage and comparing it to other members of this board, here's what I suggest you do:

1. The participating people should have a standard for filling the tank. Fill to the first click and thats it. There will be a minor deviation every fill up but thats OK. It will even out over time.
2. Record milage at fill up and gallons required to fill.
3. Record date
4. Make a very short note of type of driving during last tank of gas. Interstate, city, heavy load, trailer, etc.
5. Divide the miles traveled by the gallons used and record it. This will be your AVG MPG.
5. Record data in a spreadsheet program or do it long hand, it does not matter.
OK, that takes care of the data gathering stage. Next comes the calculating stage. I fill up an average of once a week, but the time between fill ups doesn't matter much. Wait until you get 12 fill ups before doing this calculation. If you have already have 12 recorded fill ups, you can begin!
1. Add your previous 12 AVG MPG figures and then divide by 12. This will give you an average miles per gallon over your last 12 fill ups.
2. Enter your next fill up and calculate your AVG MPG and enter it. Drop out the 13th one back and pick up the last one you just entered. This should give you a new average.
3. Repeat every fill up.

Because of differing factors such as tire pressure, ambient temp, highway or city driving etc, you really can't look at one or two tankfuls and determine anything. By adding up your previous 12 AVG MPG and dividing by 12, you will take most of those factors out of the equation because you are now looking at averages over time. This formula is called a Trailing 12 AVG MPG. You could do it over a shorter or longer cycle but the longer the cycle, the smoother your curve will be. I picked 12 because if I fill up once a week then I will be looking at a 3 month running average.
I know this is much more complex than dividing your miles traveled by the gallons used, but if you are serious about comparing your truck against someone elses and you want to take as many variables out of the equation as possible, this is one way to do it. Hope this helps.
 
#26 ·
DoctorJ said:
I filled up today the first tank in RL#2. After 380 miles it took 20.573 gallons to fill up. The guage was on the red line and not below.
You beat my mileage! Did you stay at the posted speed limits to get that far and how many days before you refueled?
 
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