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Does anybody know what effect the temperature has on the gas tank capacity? I currently have 5,163 miles on car. Filled up yesterday with two bars still showing on the "Guess Gauge" and it took 11.338 gallons. The outside temperature was about 79 degrees, and I had 539 miles on the tank and was concerned about running out. Back on February 9th when it was a lot colder (in low 40's) I had 545 miles on the tank and put in 11.117 gallons. At that time the guage was on the last bar , and had started flashing about 15 miles after it dropped to the last bar, and I also got the re-fueling message request on the screen, which was only about 1 mile from the gas station where I filled up. On all the occasions I have tried to fill the tank when car was on level or leaning slightly to the left. Also, I lift the nozzle almost to the hole cover and gas slowly until it starts to gurgle and bubble at the top of filler tube cover. My total milage to date is 5,163 and I have used 112.047 gallons for average of 46.0789 MPG. Has anyone else been able to get more than 12 gallons in the tank? I believe there was a message posted where someone put in 12.4 gallons. In other words, in hot weather when the bladder expands, is the capacity higher??? Thanks for any help because I don't want to run out, and I have been watching the milage closely. I can't quite figure out why it took so much gas when the temp was up. The monitor was showing about 53Mpg and I only got 47.54, however I did run the air conditioning on about 1/3 of the mileage on the last tank. Back in Feb when it was cold I got 49.02 mpg.

regards,
Don Good
 
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Filled up right after the "add fuel" msg. and tone. Outside air temp. 59 degrees. Filled to the shutoff click, and one more for good measure. 9.01 US gallons...

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I have 6000+ miles now. I filled up yesterday and got 12.67 gallons. This is the most I have ever put in. I had driven on the last flashing bar for about 15 miles. I always top-off (I know, I shouldn't do this for many semi-reasonably good reasons; but, I suppose none are good enough for me).

As the tank starts to top off, I have learned to pull most of the nozzle out of the small sealed area of our fillers until I have the breather port-hole (a small venturi, usually on the bottom of the nozzle toward the end) outside of our semi-sealed inlet area.

From that point, I fill slowly until I hear a lot of gurgling sounds; then I stop and leave the nozzle inserted. A funky backwash of gas kind of starts spilling into our large fill area from some small holes around the larger opening of our fill hole and seems to settle down into the tank without spilling over. Then I remove the nozzle, cap off the tank and hang the nozzle back in the pump. I can usually get close to one extra gallon in the Prius doing this.

Long story short; I don't know how close I was to running out, but I did get 12.67 in my tank yesterday.

Wayne
 
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Wayne Brown:

Apparently you are doing the same thing that I have been doing when filling the Tank. I can't see anything wrong with this topping off procedure. I dont think most people realize that the nozzle on the gas hose is 5 or 6 inches long, and if you stick it all the way into the tank and quit as soon as it shuts off, you can't be getting much more than 3/4 full or about 9/12 gallons. I think that's the reason a lot of Prius owners are only getting 9 or 10 gallons in the tank, thinking they have a full tank. Then they watch the milage, and computer display and think they can get better than 500 miles out of a tank and run out of gas. If you want to push 550 or 600, you better be "damn" sure the tank is full when you reset the trip A. I usually use trip A when I fill up and then reset B and consumption monitor everytime it drops a notch. This gives a good handle of what the actual fuel consumption is and also a better understanding as to how those 10 bars actually work--- 160 miles before first bar drops in warm weather! Well, anyway, you answered my question if you got 12.67 gallons in. I am fairly well convinced that in hot weather, the bladder holds well over 11.9 gallons. Thanks for the info!

Don Good, Ephrata PA
 
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I suspect the neck and pipe holds about 1/2 to 3/4 gals. and with warmer weather the bladder allows for the full 11.9 gals plus the neck/pipe.

Steve d.
02 super white 15000 miles.

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I understand the scientific gauging value of it, but there are EXTREMELY GOOD reasons NOT to top off. In northern California about 15 years ago, our air was worse than L.A. The reason? Not emissions. It was the vapor from auto fillups, the raw gasoline vapor.

They started putting vapor-locks and vapor-returns on the gas tanks. Now they have some new-fangled negative-pressure vapor return system on some filler valves that doesn't require a seal.

Defeating vapor returns, spilling, or even topping off where you can see the fuel at the top of the filler pipe means you've released noxious amounts of vapor into the atmosphere. If you live in a valley, this stuff collects below the temperature inversion layer and cooks into a really dangerous smog.

So I'm not trying to moralize here and say not to top off, but don't fool yourselves that there's no good reason not to. In some places (like here in California), it's against the law.

It's your decision, but make it with your eyes open.

Regards,

John
 
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John,

What you are concerned about are called VOCs (volatile organic compounds). As you may know, most gasoline fill nozzles have a vapor capture/return system to catch VOCs while we fill up. More than 95% of our fill up VOCs are captured. The last figure I saw stated that we release less than 1/4 gram of VOCs with each fill-up. You may think that the capture/return is not working whe I top off. Wrong, it still works just fine.

To put this in a more relative perspective, the State of California had more than 20 million tons of VOCs released from its asphalt highways alone last year. That would equate to 72,000,000,000,000 fill ups. That is enough for every gasoline vehicle in California to fill up more than 10,000 times each and every day of last year. With my Prius, I only fill up once about every two weeks.

If I drive my Prius 250,000 over the next ten years, I will only fill it up about 600 times. That means that in 10 years my Prius fill-ups will put about 7 ounces of gasoline VOCs into the air. I'll bet you spill more than that filling up your lawn mower every summer. And, oh my goodness, think of the dirty air your nasty lawn mower puts out not having a catalytic convertor. You probably dump more VOCs into the air in 10 hours of lawn-mowing than my Prius fill-ups will in 10 years.

Let's focus on asphalt highways or tar roofs or parking lot emulsified seal coatings or some rice patty burns or forest fires or lawn mowers or chain saws or four-wheeler recreational vehicles or boats or wave riders or camp fires or highway paint striping or camp cook stoves or jet engines or something that really puts out VOCs!
 
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Wayne Brown: Very good answer! Talking about lawn mowers, I have been using a 19" John Deer SP rotary mower for 14 years. It works great but is very heavy, and at my age 70+ is unbearable on my hilly lot (About 7000 sq ft) Just recently purchased a 18 inch Black & Decker Electric Mower (model LM-175) from Wal-Mart for 129 bucks. Has about quadruple the torque ( plus a mulching blade) of the JD rotary, and I can mow the yard in less than an hour. If I figure the time it's not running like when I re-position the extension cord, it's probably only running about 30 minutes at 750 watts, or about 3/8 of a kilowatt to mow the yard. That's less than 3 cents worth of electricity and the damn mower weighs less that 20 pounds. My minature Snauzer dog weighs 20 pounds and 7 ounces? Mower gets job done quickly with no polution except the minute amount from the Utility Company

best regards,
Don Good
 
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