Archives

So I have been thinking about how much variation can occur in the process of tracking fuel economy. Assuming the car is as close to the same each time the wind, road conditions, temperature, quality/blend of fuel (winter/summer) are just to name a few that are some I can't control.

I have been trying to eliminate as many of the variables I can control to make measurements a little more accurate. Aside from consistant driving technique, there is a variance in the way I fill up with fuel. I just realized I have been squeezing the trigger full blast until it pops and then I usually go to the next even $ amount +$1, ie it pops at $34.66and then usually go to $36.00, just to keep even $ in the totals on my spreadsheet.

Is this throwing off my numbers to be worse than they could be? Should I be filling more slowly and stopping right when the trigger pops off? Are there variances to when that trigger does pop?.....What is the best way to fill up?

Any variance in MPG for a given tank due to inconsistent filling will disappear after a tank or 2. just don’t skip recording any tanks, and in the bigger picture it will work out.

I try getting the most constant fills I can. Car parked so the fill cap is on the up hill side of slight slope. Gas pump nozzle only 1/2 open. Do not attempt over fill, I Stop filling once the nozzle shuts off.

Try to use the same station and the same pump if its possible. I always fill up with the pump handle at half throttle or flow. I think the best would be just do the same thing every time to reduce any variations in your method. People get crazy with the number of times they let it pop off. I just fill up unitl it cuts off, wait 10 seconds, fill until it pops again and i'm done.

My ultimate goal is to wait as long as possible between fillups. Hopefully one day some rich guy will buy a Volt and not like it and trade it in on some fsp and i'll be waiting at the previously owned lot with cash in hand. :)

Is this throwing off my numbers to be worse than they could be? Should I be filling more slowly and stopping right when the trigger pops off? Are there variances to when that trigger does pop?.....What is the best way to fill up?
It is generally best to fill as slow as possible but even then there is no guarantee that this will ensure the same trigger point every time. There are many things that can change the trigger point. One is simply the number of people who happen to be pumping at the same time you are. The more people that are pumping means that the fuel will flow a bit slower in each of the pumps being used at the time. When there are less people that are pumping, the fuel will flow a bit faster. The reason this matters is that when pumping faster it will cause the gas to foam more which in turn would cause the pump to trigger sooner. If more people are pumping then there is less foam and you could get a bit more fuel in before the pump triggers. This is one of the biggest reason that I top off the tank because this takes the inconsistency of the trigger point completely out of the picture. As for whether or not this can mess up the charcoal canister, it might but, I have been driving for almost 30 years and have always topped off and have never had a canister problem/failure in any of the cars I've owned that had a canister in them. I now have over 25K miles on the Prius and no problems with it either.

topping off, now does that mean that you fill until you see the gas at the same level in the filler neck every time?

topping off, now does that mean that you fill until you see the gas at the same level in the filler neck every time?
Yes, that is my strategy. I have a certain point in my filler neck/opening that I want to see the fuel at for 10-15 seconds or so before I hang up the nozzle. I want to stress that this is not intended in any way to be a recommendation that anyone else do the same as I do but rather this is just my personal preference. I should note that even this can have minute differences in fill levels due to ambient air temperatures but I go so far as to try to fill as close as possible to the same temperature as the fill-up before.

I started this tonight. I filled up a 1.5 gallon gas can with ONE gallon of gas and I'm keeping it in my car waiting for this tank to run out completely. I'll pull over, record my miles, use my can, drive to the gas station fill up to any recordable amount, should be about 8 gallons plus my ONE, then in about 4 or 5 days I'll put another ONE gallon in my can, carry it around and wait for my tank to go empty. Record the mileage, use can, go to store, repeat etc. I will then know exactly how much I used on next weeks tank and all subsequent tanks. My logs don't yet accurately reflect my mileage and this will get me so much closer.

I have a friend who uses just the one gallon can and fills up every 60 to 70 miles or so with the can only, goes to the store and fills the can again.
He doesn't practice extreme hypermiling techniques, his mileage is all mechanical mods for vaporizing fuel and standard common sense driving, if he did some P&G w NICE he would beat 100mpg every week. He is the one who turned me onto the whole FE thing with his results, years ago. I want to incorporate his mechanical ideas with Basjoos aeromods and Waynes hypermiling techniques to make the METRO MILEAGE MONSTER FROM HECK - Dale

Note, I don't smoke. (you know, fuel can in car)

Hi Leanburn:

___I follow Larry’s methods wrt fill ups. A top off is the only way I know of removing the variability and keep from having to visit our friendly neighborhood gas station maybe 1 out of 5 fill ups with some vehicles. Caveat Emptor applies...

___Good Luck

___Wayne

Before I got my SGII I topped up right to the brim. That pretty much removes all doubt on the fill level. I no longer do that. Now I just fill at a first click rate on the pump, bounce the rear of the car a bit, and do one more shutoff click. I have yet to get any close agreement between the amount the SGII reads and what the pump reads.

I'm thinking about going back to the old method, but one question concerns me. If I go back to the old method, then I'm effectively increasing my tank capacity. Should I increase the tank capacity parameter in the SGII to zero in on the fill calibration?

I always fill my tank at the slowst pump speed, wait a few seconds, and then squeeze the handle manually until the pump shuts off and then I'm done. I never "top off" the tank as I have overfilled doing that in the past and lost some gas as a consequence.

Before I got my SGII I topped up right to the brim. That pretty much removes all doubt on the fill level. I no longer do that. Now I just fill at a first click rate on the pump, bounce the rear of the car a bit, and do one more shutoff click. I have yet to get any close agreement between the amount the SGII reads and what the pump reads.

I'm thinking about going back to the old method, but one question concerns me. If I go back to the old method, then I'm effectively increasing my tank capacity. Should I increase the tank capacity parameter in the SGII to zero in on the fill calibration?
The tank capacity parameter only affects such things as distance to empty and gallons to empty calculations and doesn't have an impact on mpg calculations.

I always fill my tank at the slowst pump speed, wait a few seconds, and then squeeze the handle manually until the pump shuts off and then I'm done. I never "top off" the tank as I have overfilled doing that in the past and lost some gas as a consequence.
I think Wayne would agree that "losing" gas is a bad thing.:( However, when you treat the fuel as the precious commodity that it is, it doesn't take too much practice to overcome that nasty possibility.;)

I think Wayne would agree that "losing" gas is a bad thing.:( However, when you treat the fuel as the precious commodity that it is, it doesn't take too much practice to overcome that nasty possibility.;)

Two fills, and it was solved :D wish the waste never happened though.

I just fill at a first click rate on the pump, bounce the rear of the car a bit, and do one more shutoff click.

I always fill my tank at the slowst pump speed, wait a few seconds, and then squeeze the handle manually until the pump shuts off and then I'm done. I never "top off" the tank as I have overfilled doing that in the past and lost some gas as a consequence.

that sum's it up for me, if I don't think that first click was tank full.

I wonder the ratio of 1st or second clickers to top-off-ers in Prius and former Prius owners. Compared to the general hypermiling group.

I fill by completely depressing the handle till I'm nearing full (know from experience full will be around 35 liters), then slow down a little. When it clicks off, I'm done. I don't see the point of trying to squeeze an extra cup or two in the filler neck.

For the first couple of years I calculated mileage with most tankfuls, but now I don't bother. I've found the "trip A" mileage, calculated by the car, while a bit pessimistic, is at least consistant, and for me that works. If I see that number going up or down, I know something's changing.

I fill by completely depressing the handle till I'm nearing full (know from experience full will be around 35 liters), then slow down a little. When it clicks off, I'm done. I don't see the point of trying to squeeze an extra cup or two in the filler neck.

I would say that you really don't how much more fuel you can get in after that first click since you've never done it. Do you? In my Prius, I can get between a gallon and a gallon and a half more in after the first click. In my wife's Saturn, the difference goes up to 1.5-2 gallons. I would say this is quite a bit more than "an extra cup or two.":rolleyes:

How much extra you can get in after the first click depends on the touchiness of the auto shut-off on the nozzle, which I believe senses splash back of fuel when it's near full. I usually notice the "tone" in the filler neck climb just before the nozzle does it's shut-off, indicating the gas level is beyond the tank proper and climbing up the neck. That's close enough for me.

Its another gallon or more for me too.

I wonder if the engineers stuff the tanks too, it seems to be the only time I recall anyone saying they got anything near the stated capacity into their car.

How much extra you can get in after the first click depends on the touchiness of the auto shut-off on the nozzle, which I believe senses splash back of fuel when it's near full. I usually notice the "tone" in the filler neck climb just before the nozzle does it's shut-off, indicating the gas level is beyond the tank proper and climbing up the neck. That's close enough for me.
This is the whole point of why I top off for better accuracy. As I stated earlier, the number of pumps being used at a given time can effect this splash back which in turn determines shuttoff point. If the amount were to vary by a couple of tenths of a gallon from fill to fill the mpg would vary wildly.

It definitely is back-splash too, you can see how it works as you get closer to seeing the fuel in a top-off.

Interesting quote from the EPA.
http://www.epa.gov/donttopoff/


Topping off the gas tank can result in your paying for gasoline that is fed back into the station's tanks because your gas tank is full. The gas nozzle automatically clicks off when your gas tank is full. In areas of ozone nonattainment, gas station pumps are equipped with vapor recovery systems that feed back gas vapors into their tanks to prevent vapors from escaping into the air and contributing to air pollution. Any additional gas you try to pump into your tank may be drawn into the vapor line and fed back into the station’s storage tanks.

You need extra room in your gas tank to allow the gasoline to expand. If you top off your tank, the extra gas may evaporate into your vehicle’s vapor collection system. That system may become fouled and will not work properly causing your vehicle to run poorly and have high gas emissions.

@ quote 1, I can't have gas go back down the main nozzle as it isn't in the car when I'm topping, its an angle shot with enough just barely in the outside ring of the filler neck that if some jerk clicks the handle to round off his FSP fill a million times the drop in pressure won't waste any fuel on my car or the ground. (Not a free handed bank-shot either I don't want to risk static ignition.) The southeast isn't smart enough to use the vapor recovery nozzles so the secondary line can't suck my gas either.

@ quote 2, I don't fill in the morning if I'm not going to drive for a nice little bit and my schedule for night fills forces me to burn at least 15min so I don't have to worry about expansion either.

Very good points one needs to be careful and use a top-off method other than the one the EPA warns about, the last time I read that document it was worded for those who top-off with the nozzle still firmly seated where it clicked off.

On the charcoal canister, I haven't seen anyone before me foul theirs and it will get replaced/repaired if I'm the one person who gets mine damaged

Common sense to me says that the way you fill does not matter, be it first click, first click jiggle and one more click, first click, second click jiggle jiggle click click. Because as long as you have been tracking the milage and then use the fill amount to find MPG it should be accurate. But common sense to me also tells me that the WHERE you fill should be consistent. Different gas pumps will probably vary in their calibration so that could throw off accuracy.

Personally I'm usually a first clicker. I might try a jiggle next time though.

It is generally best to fill as slow as possible but even then there is no guarantee that this will ensure the same trigger point every time. There are many things that can change the trigger point. One is simply the number of people who happen to be pumping at the same time you are. The more people that are pumping means that the fuel will flow a bit slower in each of the pumps being used at the time. When there are less people that are pumping, the fuel will flow a bit faster. The reason this matters is that when pumping faster it will cause the gas to foam more which in turn would cause the pump to trigger sooner. If more people are pumping then there is less foam and you could get a bit more fuel in before the pump triggers. This is one of the biggest reason that I top off the tank because this takes the inconsistency of the trigger point completely out of the picture. As for whether or not this can mess up the charcoal canister, it might but, I have been driving for almost 30 years and have always topped off and have never had a canister problem/failure in any of the cars I've owned that had a canister in them. I now have over 25K miles on the Prius and no problems with it either.

Interesting quote from the EPA.
http://www.epa.gov/donttopoff/

Quote:
Topping off the gas tank can result in your paying for gasoline that is fed back into the station's tanks because your gas tank is full. The gas nozzle automatically clicks off when your gas tank is full. In areas of ozone nonattainment, gas station pumps are equipped with vapor recovery systems that feed back gas vapors into their tanks to prevent vapors from escaping into the air and contributing to air pollution. Any additional gas you try to pump into your tank may be drawn into the vapor line and fed back into the station’s storage tanks.
Quote:
You need extra room in your gas tank to allow the gasoline to expand. If you top off your tank, the extra gas may evaporate into your vehicle’s vapor collection system. That system may become fouled and will not work properly causing your vehicle to run poorly and have high gas emissions.
As I stated above, I've never had a fouled canister in nearly 30 years of doing this. I live several miles from the nearest gas station so I suppose that enough fuel gets used before I park that it creates the necessary room. I think if I were to top off and immediately park in the hot sun it could cause problems.

As for fuel being drawn back into the station system, we don't have those in any of the stations in our area.

Seems like consistency is the key: same attitude for your car, same pump when feasible. Next, my personal preference is to fill at full speed till the first shut-off, then two more "clicks" at the slowest possible rate. My MPG over the past 6 months has been quite consistent by using this method, and since the sgii install, it's calibrated to about 98% w/r to MPG computation and gallons used.

I started this tonight. I filled up a 1.5 gallon gas can with ONE gallon of gas and I'm keeping it in my car waiting for this tank to run out completely. I'll pull over, record my miles, use my can, drive to the gas station fill up to any recordable amount, should be about 8 gallons plus my ONE, then in about 4 or 5 days I'll put another ONE gallon in my can, carry it around and wait for my tank to go empty. Record the mileage, use can, go to store, repeat etc. I will then know exactly how much I used on next weeks tank and all subsequent tanks. My logs don't yet accurately reflect my mileage and this will get me so much closer.

Be careful running the fuel tank completely dry, it can cause the fuel pump to overheat and fail it can also ruin the catalytic converter. Most owners manuals warn against running completely out of gas or running the car when its not running properly because of damage to the catalytic converter. I think that is what happened to the catalytic converter on my '96 Contour. I was on a trip and had a short in the electrical system which let the battery get extremely low and the car was running bad and backfiring. Soon afterward is when the catalytic converter went out. I think it causes them to overheat ruining their catalytic properties.

topping off, now does that mean that you fill until you see the gas at the same level in the filler neck every time?

I also top off the tank. I've been driving for 32 years and never had any problems with the vapor canisters. My '88 Escort has 483,000 plus miles on it without any problems and I've had several other cars with 100,000-250,000 miles.

I'm thinking about going back to the old method, but one question concerns me. If I go back to the old method, then I'm effectively increasing my tank capacity. Should I increase the tank capacity parameter in the SGII to zero in on the fill calibration?

My '97 Escort has a 12.8 gallon tank and since I top off I just went to 13 gallons on the calibration on the SG-II and figured anything over 13 gallons would just be like a reserve. It also has a fuel light that comes on when the tank gets down to 2 gallons.

I would say that you really don't how much more fuel you can get in after that first click since you've never done it. Do you? In my Prius, I can get between a gallon and a gallon and a half more in after the first click. In my wife's Saturn, the difference goes up to 1.5-2 gallons. I would say this is quite a bit more than "an extra cup or two.":rolleyes:

My '88 Escort and '97 Escort will hold 1-2 gallons after clicking off the first time. My wifes '87 Chevy Celebrity will hold 4-5 gallons more. I've put as much as 14.02 gallons of gas in my '88 Escort which according to the owners manual has either 12.9 gallon or 13 gallon tank I forget which.