False alarm check engine light thanks to gas attendant...

No permanent damage. You just lost a little gasoline to evaporation in that week. It became air pollution. In my opinion, topping off in moderation is unlikely to do damage, but regularly taking it to the extreme will indeed cause damage.

 

Kindly ask the gas station attendant to not over fill the tank. Ask them to stop pumping when the pump kicks off the first time and to NOT top off the tank. Then after you leave the station, check to make sure the cap is tight. Just turn it to the right until you hear or feel the click. Once it does that, that is all that you need to do to make sure the gas cap is on there correctly.

FWIW, Oregon does this to protect folks but sometimes it seems to cause more trouble than it is worth.

Best of luck to you and "Welcome to Prius Chat"!

 

When in Oregon, I show no hesitation to do the gas door work myself. Sometimes the credit card reader too. As long as I don't touch their pump hose and nozzle, I don't believe they can complain.

Wasn't topping prohibited several years ago? If they still do it, against your wishes, raise a stink about it! Go to station management. If management blows you off, report them to the state.

A potential problem, flooding liquid fuel into the evaporation control system, applies to nearly all modern cars. It is not specific to Prius.

 

you might want to explain that/
since two years I top off until I see the gas standing in the filler neck (that's pretty much two gallons more than when it shuts up automatically); that means in my case 100 miles more range/
never had ne problem or codes or whatsoever/

 

I have -always- filled Pearl S until I see liquid fuel in the filler tube just down from the gas cap. It has never caused a problem. So I "top up" to the extreme with no problems. Always did the same with the GII (Pearl) as well, and again, with no problems. Why? Simple, it gives me 6-10 litres of extra fuel and about 100 km or more extra range. Doing this does not change the amount of fuel vapour that gets into the air (we don't have the silly vapour vacuum systems some regions have). If done reasonably it does not overpressure the fuel system (fill up at the beginning of a trip not the end).

There are lots of wags who like to think they know the world will end and know what will cause it.

 

It really does matter, and you shouldn't top off. The manual of Prius and virtually all cars tell us not to do this.

As you saw from this thread, a loose-fitting gas cap will cause an emissions warning. Why? Because fuel evaporation causes substantial air pollution. So your vehicle's fuel talk and fuel system is sealed against evaporation -- as long as the fuel cap is in place. The evaporated fuel rises up from your tank and the fumes are caught inside a charcoal canister. During vehicle operation, valves open which blow these captured fumes into the engine, which burns the fumes along with the gasoline.

If you overfill your gas tank, gasoline can slosh into the vapor recovery lines and into the charcoal canister, destroying the charcoal and ruining the evap system. You may then be faced with replacing the charcoal can, plus, in the meantime, you've been polluting the air, you no-good-scoundrel. So please do your part to reduce air pollution, by not overfilling your gas tank. And if a clown at an Oregon gas station does this, tell him not to and report him or her to the State's Department of Environmental Somethingoranother.

 

Gasoline in the charcoal filter WILL NOT harm it! I wish people would stop repeating this nonsense! What exactly do you think the charcoal filter does with the gasoline vapour? Why it turns it into liquid gasoline. Amazing. If gasoline in the filter damaged it then it would be curtains right from the start.

The ONLY time overfilling will cause harm is if the tank is absolutely filled and the cap replaced, with colder than ambient fuel and the car is left off. Then the fuel will expand and pressurize the tank, more than it normally is pressurized. This -can- cause hoses to pop off. It's rare, but it does happen.
It takes a very determined individual to fill the tank/system this much (I've done it, and watched the expanding fuel flow out the filler as it warmed up - on a Mazda RX-7). In the Prius, you have to fill it -full- (fuel at cap), wait as it seeps into the evap. system, fill again, etc. etc. at least 5 to 10 times before it's actually -full-. It takes about 10 minutes of fiddling to get it absolutely full. I never do this, by the way. I fill to the cap once, replace the cap, and drive the car. This ensures the tank is never actually completely full.

Chill out people!

 

Topping off was banned in Oregon as of July 1, 2009. If the attendants persist against your warnings, report them to Oregon DEQ at 1-800-452-4011.

Here are some links:
Topping off gas tanks now banned in Oregon | OregonLive.com
Oregon DEQ: Gasoline Vapor Recovery Program
http://www.deq.state.or.us/aq/permit/vapor/TopOffSign.pdf
http://www.deq.state.or.us/aq/permit/vapor/TopOffBanFlyer.pdf
http://www.deq.state.or.us/aq/factsheets/NoTopOff.pdf
Don’t Top Off the Tank: New Rules for Oregon Gas Stations

I am not going to argue the point about whether it is bad or not. I'm just pointing out there should not be anything special about the Prius on this matter. As best I know, it is not meaningfully different than most other modern cars.

 

Actually, while it doesn't harm the filter, it will plug it for awhile, stopping it from functioning. So I guess it's "bad" for awhile anyway. Once the filter drains the system is "back to normal".

 

Topping off will not hurt the Gen III Prius. I've been doing it for almost 120,000 miles...to the brim. Even if you are not allowed to pump your own gas, no one can stop you from checking the cap before you leave.

 

David,
They have decaffeinated blends that taste just as good as regular coffee.

I never soaked a charcoal canister in gasoline. I just followed the directions and explanations I've read many times. And that explanation is very commonly given. Your explanation may well be right, but I am not going to test the theory. All vehicles warn against the evil of overfilling, service stations here in California understandably warn against it, and Oregon has even outlawed it. (In California, our service stations all have evaporative recovery built into the gas hoses, which fit tightly against the filler cap. If you overfill, the gas can just pour up the neck and then up into the hose, and when you disconnect the hose, gas will gush out of the hose and all over your car's paint, the ground, and you. Of this, I am foolish enough to have empirical data of my own.)

Clearly, some kind of awful terror will befall those who overfill. And, since I hate decaf, I will leave it at that, remain ignorant, and shut off the pump with a single click.

 

Oh, the wickedness! You spent too long in Mordor!

 

Nope...work, live and play in reality.

 

Shutting off at the first click works for me. The pump says it's done, I don't argue.

 

I look at the pump display vs what I expected. Sometimes it cuts off early -- way early -- so I know there is more room remaining to the normal fill point. Resume filling to the next auto-shutoff. And if I'm at the start of a long trip, maybe another half gallon too.

But in places like Oregon, without self-serve, attendants darn well better have the driver's permission before doing any (illegal in some places, such as Oregon) topping off.

 

The blessing of higher gas prices means less fuel needs to be added to round the purchase off. How many cash paying customers don't mind pumping more gas after shutoff when the purchase is $x.97?

How does one document a complaint in Oregon? Can the pump jockey file a cross complaint against the driver for pumping their own gas?

 

Some of you folks at both extremes of this oddly controversial issue might consider sensible moderation. Given that the tank can, according to StarCaller and others, safely hold two gallons after first click, I don't feel terribly worried or guilty about adding my usual 1.5 gallons. That should allow adequate room for thermal expansion, especially if I'll be burning off a significant amount before parking. On the other hand, I don't risk flooding the canister by taking an absurdly long time coaxing the last possible drop into the filler neck, the Gerdes technique. Adding my 1.5, in drabs of about 0.07 to 0.11 at a time, takes long enough.