Prius topped off gas by the gas attendant...

Or moving to New Joyzee, too! They won't allow you to touch a fuel pump there, either!

 

I have always filled till I see fuel in the filler tube. I have had no issues. One warning though. If you live in an area where the air temperature is much higher than the ground temp (about 50F) it's good to leave an air pocket to allow the liquid fuel to expand as it warms up. The Prius leaves way too much by design, at least in any location I've been to. It's safer that way so that's probably why Toyota engineers did it. Some of us like the extra distance we can go when we fill all the way. I go 200 km before the first pip goes away. The car usually thinks we can go almost 1000 km on a tank. But as I already said, when (IF) it ever gets "hot" here I'm a little more conservative. In Edmonton 30C is rare (80F), and 40C is almost unheard of. Of course -30C is common and -40C happens at least once a year.

Be a little more careful with a GII Prius with the bladder fuel tank. IF the fuel expands enough to expel all vapour/air in the tank you will have hydraulic lock, and any further expansion WILL damage the tank assembly - for example pop hoses off inside the tank. NEW TANK TIME!

 

Gas pump nozzles are designed to shut off automatically once the fuel reaches their end tips. When you top off your tank, where do you think the extra gas will go? Well... It goes right back to the gas stations' under ground fuel tank ...

Please read this before filling your next tank: Don't Top Off Your Gas Tank! | Mid-Atlantic Air Protection

 

Disregard my last.

I keep forgetting the strong Green Peace demographics here. If you top off, you are personally responsible for destroying Mother Earth. Don't do it, and report anyone who does (even your child) to the EPA for stiff fines and/or incarceration.

 

They forgot to mention that one shouldn't look for the level of gasoline in the tank with a lighted match. The sad part is there are people that actually believe that page.

 

You have been lucky so far.
Your luck will run out eventually and it likely will be expensive when it does.
Regardless of your personal experience, it is NOT a wise thing to do.

How do you do that when the pump has a vapor recovery boot or a splash guard on it ??

And after we have gone though ALL of this discussion, not a single person has suggested that the young attendant who started this discussion should be reported to his boss. He should be. Just because his bad habit didn't cause you a problem doesn't mean that it won't for others.
Odds are that it WILL.

 

There's usually one jockey to eight pumps around here, so when they start the pump going, I get out of the car and finish the transaction 'cause you never know when he's coming back.

 

Maybe misguided, but I've always assumed gas tank cramming by attendants was at the behest of station managers.

 

You are misguided. My dad owns and runs a gas station. Usually there is not much of a profit margin, especially at stations that charge the same for credit cards as they do for cash. Credit cards take 7-8 cents off of the profit margin. In NJ at least, you need 12-15 cent/gallon profit margin, assuming decent sales volume for the day, to handle overhead/pay employees, etc. This is not always possible if local stations start a pricing competition. Selling other items at the station helps with generation of profit and to offset low gas sales profit days. Having one or more diesel pumps helps because it mostly goes into trucks with large tank volumes. My dad jokes sometimes that people like me (who put at most 10 gallons in the tank and pay with a credit card) are costing him money.

In the distant past when I helped my dad it was actually the customers that asked me to put more in to get the cost value to the nearest dollar so they don't have to drag around change. But that was before credit cards became popular. The upside of credit cards becoming popular is that it's been a long time since my dad's station got robbed. I guess the robbers have decided the risk/reward ratio no longer benefits them.

 

Jim - To believe in what EPA said in its website requires some knowledge, not faith! Please don't feel sad !

Fuel Dispensing Nozzle (or FDN) does look simple, but it has hundreds of parts inside. To understand how the FDN can shut off automatically when the fuel reach its end tip would require some engineering knowledge, or at least to be able to understand well of Fluid Dynamics, specifically, Bernoulli's principle.

Please open the link here and click on the images, you can see the cross section cut of one of the modern FDNs: Patent US5394909 - Vapor control valve - Google Patents

EPA has changed the vehicle emissions control requirements from time to time since the day they were established. Fuel vapor released to the atmosphere had been the major contribution to the environmental pollution. The EPA has tried very hard to keep the air clean for you to breath. From the early 70's, all vehicles must have PCV (Positive Crankcase Ventilation) valve to feed the unburned fuel back to the engine instead of releasing it to the atmosphere. There have been many changes to the design of the new cars since then. Like all gas tank caps must have check valves to let the air in only. Since fuel vapor in the tank can not escape with the new caps, charcoal canisters have been used to capture the vapor and then release back to the engines when needed. EPA also has very strict regulations for the fuel dispensing systems. When you are pumping gas,the liquid fuel will displace the vapor inside the tank and FDN must be able to capture it. It supposes to suck the fuel vapor back to the underground tanks but if the liquid fuel gets in its way, it doesn't know any better and will not refuse to suck it in too.

Please watch a short video below to see how a FDN works:

 

One thing's for sure, plenty of entertainment on PC if you need a good chuckle.

 

<rant on>

So how long will it take for my luck to "run out"? It's been 50 years so far.

No silly vapour recovery boots here (like they do -anything- but make filling up harder! Splash guards are no problem.


As for "the gas goes back into the stations tank" (I paraphrase), not likely. There is no path in Alberta or B.C. We don't have the ridiculous "fuel vapour collectors" some US states mandate. And NO the nossles don't take in the vapour. That is why the rubber correlated tubes surround the nossle right to the fill tube end. The vapour is sucked in through that, and cycled to a condenser system. I don't think fuel would go through that system, it's too heavy. But again, we don't have them here.

Finally, the nossle does NOT shut off because it senses liquid fuel, it shuts off when there is enough vapour back pressure to cause that. The back pressure is generated when the fuel plugs the vapour return line in the cars tank, most of the time causing an increase in vapour pressure (air and fuel vapour) coming out of the fill tube. That vapour return line vents just down from the end of the fill tube, and when the nossle is fully inserted it does not see that vapour as it exits close to the handle of the nossle. You can see the vapour exit port if you look closely inside the fill tube (use a flashlight not a match)! Sometimes, if the fill rate is high enough, it causes fuel foam to reach the nossle, and that will trip it. It can also be generated if the nossle end is immersed in liquid fuel, but if it waited for fuel you would have spills ALL THE TIME! Which is why, if you leave the nossle all the way in, you can't top off unless you want to spend 30 min. doing so. It takes that long to completely fill the tank and fill tube (trip, reset, trip reset, etc etc.). Oh, and yes, you also get lots of liquid gasoline in the carbon canister. This WILL NOT damage it! What do you think the vapour that is fed into it turns into?
Because it shuts off when the vapour return line is plugged (by liquid fuel down in the tank or in the lower end of the fill tube) the cars manufacturer can somewhat control when that happens. Some allow a 10% "expansion volume", some as much as 20%. The Prius is in the upper end of that. So after the first nossle trip I can add 5-8 litres more fuel to the 45 litre tank before I see fuel in the filler tube. The amount depends on the fill rate. At any rate that gives me an additional 100 to 150 km cruising range AND accurate fills. I always know how much fuel the tank took to fill within about 10ccs.

<rant off>

 

Just stumbled on this thread this morning and was reminded of what happened to me when filling up this week...

I locked the handle as the gas was pumping, and was standing next to the car waiting for it to fill and was looking at my phone. When the tank filled, the pump didn't shut off like it normally does - it just kept pumping until I reached down and squeezed the handle. As you can imagine, it made a mess.

I have been driving (and pumping gas) for 25+ years, and I don't remember ANY time where a pump failed to shut off when the tank was full.

In hindsight, I probably should have told the station attendant about the problem, but I was running late for work. Perhaps the nozzle was defective or failed?

 

^ Isn't there something on the pumps about not using a cell phone when pumping gas? Yeah, I would alert the station about that pump.

And to David: filling to the neck is not a prerequisite for accurate calculations. It doesn't hurt, but consistent behaviour, say just stopping when it clicks off, will give fairly accurate results, and that accuracy goes to more-or-less 100% once you've done two or 3 refills: any inaccuracy in a single tank quickly cancels out with the next tank.

 

The nozzle is defective, and David Beale is correct about the canister. There were a few cars in the past where the recovery system had a flawed design and the manufactures lawyers blamed it on topping off to avoid lawsuits. I have been pumping and topping tanks for almost 40 years and the only problem I ever had was with the Wife's 05 Durango, where is splashed back on the first click. A subsequent documented Service Bulletin fixed that.

 

Golly... that means it can suck gas through the air between the end of the nozzle and the flexible seal made at the top of the filler pipe. The top of the filler pipe is where the suction pump operates so if you fill to over flowing it will indeed pump gas but not at the second or even third click. Don't believe every thing you read, especially on the internet.

 

The flexible plastic piece you are talking about is called "Nozzle Splash Guard". It is used to prevent fuel from splashing back onto customers during fueling. Please read the patent about fuel-dispening nozzle's vapor control valve in my reply above. Anyway, this is the introduction part of the patent:

Vapor control valve
US 5394909 A

Abstract

A vapor valve for use in conjunction with the fuel dispensing nozzle for capturing vapors returned through the nozzle to a storage area, the nozzle incorporating a body, a spout extending forwardly therefrom, and the nozzle having an operating latch pin and housing for normally providing for opening or shut-off of the nozzle during a dispensing function, a vapor passageway extending through the spout, communicating into the latch pin housing, and extending through the nozzle body for return of vapors back to a storage area, and a latch ring operatively associated with the latch pin and providing for opening or closure to the vapor port of the latch pin housing to furnish its opening while fuel is being dispensed for return of vapors to a storage area, or when the fuel dispensing function is curtailed, providing for an upward shifting of the latch ring within the housing for closure of its associated vapor port and preventing the escape of vapors to the atmosphere.

Here is the link again: Patent US5394909 - Vapor control valve - Google Patents

 

This is what we have here.

 

I hope you feel better now......but most of that post was just a waste of time......and clearly shows that you know NOTHING about how the auto shutoff nozzles really work.
The work when tiny little holes near the end of the nozzle get plugged with liquid gas.
It works for motorcycles and gas cans too.

Acting like you are some kind of "expert" on things that your really know nothing about gives you a bad reputation. It does not get you extra points for yelling the loudest.