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03-16-2010, 04:22 PM | #1 |
Drives: 2008 Yaris Sedan Join Date: Feb 2010
Location: Oklahoma City, OK
Posts: 323
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Accurate fuel fill without topping off?
Traditionally, on my cars I've always had a standard procedure for ensuring an accurate fuel fill. Run the pump till it auto-stops. Top it off. Bounce 15 times. And then top off again. However:
1. Topping off results in increased pollution from vapor. 2. I've read on this forum that topping off the Yaris can cause problems with the canister/vent system. (Is this true, I wonder?) 3. Topping off the Yaris involves tediously putting in over a gallon of extra fuel, which takes a while and is a real pain in the cold and wind. 4. The way the filler is designed, it's hard to top off without getting fuel on the paint every time. So... is there a better way to do this while preserving accuracy? I travel a lot, and so always using the same pump is not possible. -Steve |
03-16-2010, 08:14 PM | #2 |
Is now a Corolla S Owner
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Steve:
The error in fuel mileage calculation due to the degree to which the tank is filled should be minimal over several tanks of gas. The error should cancel itself out over several tanks. I have read the same thing that you have about how over-filling can be harmful to the fuel evap system, so I stopped doing that. When the pump kicks off the first time, I remove the nozzle. Tom |
03-16-2010, 08:24 PM | #3 |
Drives: 08 Yaris Sedan Join Date: Oct 2008
Location: California - Bay Area
Posts: 2,773
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You should never top off gas. Your going to destroy the charcoal canister.
1. you're paying for gasoline you aren't using, as it is sucked back into the pump's vapor recovery system 2. gasoline can drip from the nozzle onto your car or on the next customer. not only will this damage the paint and leave you or your car smelling like gasoline, these released vapors aren't recovered go into the atmosphere. (besides a slight fire risk...) 3. gasoline vapors are unhealthy to breathe. (known to cause cancer) 4. topping off your car's fuel tank may cause fuel to enter your car's vapor recovery system (charcoal canister), poisoning it and causing it to be unable to function properly, which may get you a check engine light on your car besides putting out more emissions and costing you more money to repair it. 4. As the temperature changes, your fuel needs somewhere to expand to. If you top off your tank, this expanding fuel/vapor is forced into your vapor recovery system (see above). So in the end its not at all worth it to top off your gas. Thats why at the gas stations they have signs everywhere saying not to do so. I would just run the pump till it clicks and stops. Hang the nozzle back up and put your gas cap back on. Any discrepency will be so minute. If you want to get the most true acurate readings i would suggest purchasing a ecometer. Then you can graph your monthly mpg adverage there will be less likely error over longer period of time. Maybe 2 percent.
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03-16-2010, 08:24 PM | #4 | |
Drives: 2008 Yaris Sedan Join Date: Feb 2010
Location: Oklahoma City, OK
Posts: 323
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Quote:
But it is nice to have that extra gallon of fuel, and the extra range it represents. -Steve |
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03-17-2010, 12:13 AM | #5 |
Drives: 08 Yaris sedan auto / Fit auto Join Date: Oct 2009
Location: northeast
Posts: 2,897
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1 click of nozzle at full speed of fuel . Try to use same pump at each fill . The ECO-METER has been off by about .5 since less need for idling in morning to defrost windows . More the idling the wider the margin from calculated m.p.g. .
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03-18-2010, 12:33 PM | #6 |
Drives: Black XA not yaris but close Join Date: Jun 2009
Location: DFW
Posts: 48
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I stop at the first click, I fill at the first click on the pump handles so its slow. The wide open click on the gas pumps tend to vary a lot. The slowest doesn't vary much from station to station.
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03-18-2010, 03:45 PM | #7 |
Half a Bubble Off Plumb
Drives: 2009 Yaris Sedan Join Date: Mar 2009
Location: Bristol, Tennessee, USA
Posts: 1,593
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That's been my assumption, that the slow fill is more reliable. So I fill it wide open till it clicks off, wait a few seconds for the bubbles to clear out, start it back as slow as it will go and let it click off once more. Never adds more than about 1/10 gallon, and seems to be consistent.
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03-18-2010, 03:56 PM | #8 |
Steals terrorist's lunch
Drives: 2007 Yaris Liftback Join Date: Mar 2007
Location: Reno, Nevada, USA
Posts: 1,299
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I always just fill on the slowest setting and stop at the first click, then turn the nozzle upside down to get out anything left in it.
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03-18-2010, 06:35 PM | #9 | |
Banned
Drives: '10 Yaris5drHB+99 4runner LTD Join Date: Sep 2009
Location: NE
Posts: 672
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Quote:
they vent......into........the intake. so, no one is paying for any gas they do not use. |
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03-18-2010, 08:28 PM | #10 | |
Drives: 08 Yaris Sedan Join Date: Oct 2008
Location: California - Bay Area
Posts: 2,773
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Quote:
http://www.sbcapcd.org/edu/dtofactsheet.pdf
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03-18-2010, 08:59 PM | #11 |
Drives: 2008 Yaris Sedan Join Date: Feb 2010
Location: Oklahoma City, OK
Posts: 323
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Hope you don't feel I'm picking on you, YarisSedan. I appreciate you response. But I can't help commenting upon this lovely public service publication aimed at the general public.
There's more than a bit of propaganda in that link, mixed with some valid points. But I'll just put some numbers on one of the points mentioned. After the first click-off, the Yaris tank can still hold another gallon of fuel. (Slightly more, but let's keep the numbers round.) One mole of a gas occupies 22.4 litres at standard temperature and pressure. The average molecular weight of (the components of) gasoline is 108. So 22.4 litres of gasoline vapor weighs 108 grams. That's 4.8 grams per litre, or about 18 grams per gallon. Liquid gasoline weighs about 3000 grams per gallon. So the lost vapor from the top off works out to about 1/170th of a gallon. Hardly enough to break the bank. It's worth about 1.5 cents. So if you're the sort who bends down to pick up pennies and takes them home to put in a jar then this might be significant to you. Note, however, that likely about half the vapor is captured by the Yaris' capture system. So you're probably only saving about 3/4 of a cent, in reality. Another amusing highlight from the link is this: ==== I picked up the nozzle and gas spilled out. What should I do? It’s likely that someone before you topped off a tank and caused this problem for you, and the damage is done. The nozzle may still be able to function properly, but if you notice any more problems, tell an attendant at the station, and use a different pump. ==== Because after such abuse as the thoughtless sociopath in front of you at the pump has inflicted upon it, the nozzle may not ever be able to function again... :-0 -Steve Last edited by sbergman27; 03-18-2010 at 09:29 PM. |
03-19-2010, 12:52 PM | #12 |
Drives: Black XA not yaris but close Join Date: Jun 2009
Location: DFW
Posts: 48
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How can I reduce my risk of breathing gas vapors at
the station? Use the nozzle’s hold-open latch to pump the gas continuously, and stand upwind (but stay close enough to monitor it). Always remember to remove the nozzle before driving away – and be sure to tighten your gas cap. Ha ha I started to fill my tank and there’s a strong smell of gasoline. What should I do? Tell an attendant at the station, and to report a problem, call the APCD at 961-8800. |
03-19-2010, 10:47 PM | #13 |
Drives: 2009 Meteorite Metallic LB MT Join Date: Oct 2008
Location: Southeast Wisconsin
Posts: 810
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Is that Pam after the breast reduction?
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03-19-2010, 11:34 PM | #14 | |
Drives: '08 Yaris Join Date: Oct 2008
Location: SoCal (Jamul)
Posts: 97
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Quote:
By the way, the extra room in the tank is meant to leave room for expansion and sloshing, and to prevent the flooding of the charcoal canister (part of the car's vapor recovery system). So it's not a good idea to overfill the tank. |
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03-20-2010, 10:38 AM | #15 | |
Banned
Drives: '10 Yaris5drHB+99 4runner LTD Join Date: Sep 2009
Location: NE
Posts: 672
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Quote:
of the coaxial line onto my paint from the dub who gassed up before me and it got sucked up the hose, but not all the way |
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03-20-2010, 10:41 AM | #16 |
Banned
Drives: '10 Yaris5drHB+99 4runner LTD Join Date: Sep 2009
Location: NE
Posts: 672
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heh
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03-20-2010, 10:58 AM | #17 |
Drives: '09 Yaris Sedan Join Date: Oct 2009
Location: Western N.Y.
Posts: 75
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Filling to the very top is nice if you have all the time in the world. Plus you are hauling the weight of that extra fuel. Keep track of all your gallons and divide it into a total mileage from your odometer and the refill amount won't mater. Base it all on the mileage from your next fill up. Reset the B trip odometer and keep all your gas receipts. Then add up all the gallonage and divide that into the trip B reading. Changes in driving habits, traffic patterns, weather, etc... will all blend in.
doc |
03-20-2010, 11:03 AM | #18 |
Half a Bubble Off Plumb
Drives: 2009 Yaris Sedan Join Date: Mar 2009
Location: Bristol, Tennessee, USA
Posts: 1,593
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It'll still clog up your charcoal canister.
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