Gas Fill Up question

So why do they include a charcoal canister in the system? If the system were entirely closed there would be no need; and that canister is intended to be saturated with fuel vapors, not liquid as happens when one tops off.

 

When you overfill, gas is pumped into the vapor canister (which prevents it from doing its job to reduce emissions).

Does anyone know how the gas gets out of there or what the capacity is?

That could be the answer to the erratic gauge behavior some people have witnessed. A sudden purging of the gas it is holding (from canister to tank) would definitely cause measurement confusion.

 

the bladder when empty, has NO AIR IN IT. therefore when you fill up, there IS AN AIRTIGHT SEAL. The metal tank that holds the bladder is vented in the usual way.

 

Umm, vented, why?

Gasoline goes into a tube connected to the bladder. What's getting into the tank proper that needs venting?...

 

The bladder

venting is in the unlikely case of a leak. also if the tank wasnt vented in some way there would be a build up of pressure when the bladder is filled. if everything is working properly, the only thing you will be venting is air. at no time will gasoline vapor be vented to the atmosphere. this is one of the reasons for Prius' reduced polution contribution.

 

Just to add another comment, my Prius, produced in March 2004 does not a have a fill up problem. I get about 48 or 49 mpg, and I fill up at one of two gas stations where I know the price is (relatively) low, and expect to put ballpark 9 gallons in the tank.

I think the most I put in was 10.2 and the least was 8.5 gallons.

The indicator is at the last bar when I fill up. I plan the fillups so I know that I can stop at the "cheaper" gas stations. I figure that I will save oney in the long run.

Oh, yeah, I fill up using the slow flow setting, and do not go past the pump shutoff, if the volume is about 9 or 10 gallons. In the long run, I will have an accurate measure of mpg. I feel that it is best not to put too much emphasis on a single tank fuel economy.

When i speak to someone who DOES NOT own a Prius, I mention 48 mpg and they say "WOW", and I mention 480 miles per tank, and they say "I wish my car wnet 480 miles between fillups!"

Sports car enthusiasts tell me they get 28 mpg, and are very happy.

 

Ox:

you got the right idea. it still amazes me with all the hype over inaccurate gas gauges, small gas tanks, "limited" ranges etc.

i think we Prius owners have become royally spoiled.

also in the "side shot of gas tank" thread there is a great illustration of the design of the gas tank. As you will see the only way that the charcoal filter comes into play is when the bladder is overfilled.

besides the tube filling the bladder there is an overflow tube that could conceivably reroute gas from the filler tube through the overflow tube, through the charcoal filter and INTO THE GAS TANK. There is no way for the gas inside the tank to be rerouted back to the bladder and therefore it cannot be used for the car.

so for all you guys out there that think you are benefitting the environment by driving Prius' are negating any possible benefit because of the polution you are causing by overfilling your tank.

 

Um, first off, I don't think Toyota engineers were stupid enough to build it so that if you overfill, gas goes into the tank between the bladder and the metal. Trust me, every corporation out there sees America as the stupidest country in the world - why do you think we don't get half the Nokia phones that are so cool?

Anyway, if you look at the diagram, the bladder does not directly connect to the charcoal canister - it is a line above the bladder line.

Any engineer in their right mind would design a car bladder, when overfilled, to go the only way it should - back onto the filler, back out the way it came. That way, it's the fault of the user, not a design flaw and blamed on bad engineering.

Just my 2 cents. And, I don't overfill my tank. I fill it. Everyone else underfills theirs, and that's fine for them.

-m.

 

rflagg:

ummm what you said is right...but you are only looking at half the picture.

directly from the filler tube there is an overflow with a reservoir with two outlets that leads to the fuel pump the other to the charcoal cannister then to the tank.

the reservoir is there to stop any fluid from flowing into the charcoal cannister. however, with air tight seals of gas pumps, it is easily possible to overfill the
reservoir thus forcing fluid into the charcoal cannister and into the gas tank.

unlike normal cars, the charcoal cannister is not necessary and is only present in case of emergency ( actually its there in case of stupidity) if all systems are working and the tank is not overfilled, the charcoal cannister plays no role whatsoever. It is simply another safety measure that Toyota engineers rightly (obviously) thought was necessary.

Now as for your statement that anyone would design the overflow to only go back to where its supposed to e.g. the bladder...

well hate to burst your bubble but the overflow comes into play because there is no room left in the bladder. under best case scenarios, the overflow will be minimal and simply drain back into the fuel pump. but in other cases it will drain into the tank. this being a slightly better choice than ejecting it out the filler hole.

 

As stated before though - after the first click off, you pull the pump out to allow the air to escape so there will be no splashback, thus removing any airtight seal.

-m.