is "topping off" after fill up harmful?

[Joe1]

A mechanic once told me that continuing to fill the gas tank after it automatically stops can be harmful. I forgot the reason why.

I live in NJ, the land of "full service" gas where it is illegal to pump your own gas. Costco, WaWa, and Quick Chek gas attendants rarely if ever overfill the tank or continue to pump to make it an even amount such as $19.21 to $20.00. However, l often experience this behavior at independently owned stations and therefore try limiting my gasoline purchases from corporate owned retailers where the employees are properly trained.

Am l overthinking here or is the practice of continuing to feed gas to a full tank detrimental? I can probably do a search, but thought I'd get the interesting opinions here.

 

[RooflessVW]

It can kill your carbon canister and force liquid fuel where it doesn't belong.

 

[simple_gifts]

+1; i believe you can also potentially cause a CEL if the canister isn't working

 

[Pelican]

What RooflesssVW said, if you round it up to the nearest nickel it may be OK but beyond that you may flood the canister which will cost you a fair amount to replace.

 

[69GTX]

Before the days of carbon canisters and numerous credit cards many more of us topped off to the nearest dollar or 50c.

 

[Wolf359]

Depends on the car. Some have no problem with it, others do. Hence the standard advice not to top off in case your car doesn't like it. Some of them do have room for a little bit more. I believe it's the pump that senses the air pressure that causes it to shut off so that's why it could also vary from pump to pump.

 

[Danh]

If you're going to drive a couple miles and park it for a while, don't. If you're on a road trip or will be driving it 10 miles or more before shutoff, go for it.

 

[slacktide_bitog]

You are correct that topping off is indeed harmful.

The NJ stations do it because they don't want to make change. Also, NEVER USE CASH!!!!!!!!! They are less likely to top off if you pay with a card, but it does still happen sometimes. Stick to Costco, Wawa, and Sam's Club. Costco has signs on the pumps saying not to top off.

 

[Brybo86]

i routinely add an extra 2-3.5 gallons to my 2008 Honda Accord after the pumps auto shutoff (usually only do this if i have the time ((because you have to hold the trigger at about 1/4 flow)) and or we are on a road trip and trying to stretch a few more miles between stopping and waking up the kids) (don't do this if the temp is -22F outside like this week)

been doing this for 6 years..... and 150k miles
never a CEL...
i can go about 160 miles before the fuel gauge needle even moves....

my 1995 Lexus LS400 will only take about 0.5 gallons extra after the pump auto shutoff

i think all the signs on pumps are because they don't want people spilling a drop of gas and its god awful effects on the environment

i don't spill because well that would be wasting money.

 

[Joe1]

Originally Posted by slacktide_bitog
You are correct that topping off is indeed harmful.

The NJ stations do it because they don't want to make change. Also, NEVER USE CASH!!!!!!!!! They are less likely to top off if you pay with a card, but it does still happen sometimes. Stick to Costco, Wawa, and Sam's Club. Costco has signs on the pumps saying not to top off.


Good advice about not using cash. Costco, Quick Chek and Wawa charge same price cash or credit. (Costco does not accept cash). I buy Costco gas 80 pct of time as it is top tier and usually cheapest.

 

[Uphill_Both_Ways]

Costco's pumps are set to fast flow even with the gentlest trigger squeeze, making it more difficult to fill up past the auto shutoff.

However, I know of two pumps at one of two Costco gas stations in Winnipeg that can be more precisely regulated and try to use them when it's not two million below zero and no one's waiting behind me. But even then I can add a couple of litres to the tank more easily at those pumps.

.

 

[mclasser]

I don't top off. I cringe when I see other people do it. Whenever driving thru NJ, I avoid stopping for gas there. If I have to, I tell the attendant not to top off.

 

[y_p_w]

Depends on how full it actually gets. Once it stops there may or may not be some additional room in the tank.

However, it's generally not a good idea with modern vapor recovery fuel nozzles with hoods. They're designed to prevent fuel vapors or liquids from leaking. Often when someone insists on pumping more after it stops the first time, it will end up sending fuel back into the recovery system. In the early days I've heard of reports where people just kept on pumping after it initially stopped, it started putting in 4-5 more gallons, and when the user stopped and pulled it out quickly the fuel started spraying everywhere under pressure.

Other people do odd things such as pump with the nozzle upside down. I've heard of large spills after it overfills, since they're designed to stop when oriented the correct way. I'm not sure exactly how it's supposed to work when someone has one of those oddball filler holes that point straight up.

In California I remember there used to be fuel recovery nozzles that didn't have hoods, although most did. They would have holes that would suck in vapors, but where it wouldn't necessarily suck in liquid fuel if overfilled. I'm pretty sure they were gone when the state instituted a higher standard for vapor recovery. They looked like this:

 

[JC1]

Originally Posted by rooflessVW
It can kill your carbon canister and force liquid fuel where it doesn't belong.


+1. I've seen other bozos at Costco trying to get every last drop in their tank. One guy was an uber driver. Not worth the potential damage it may cause the evap system. If you need that much extra gas get an extra Jerry can and fill it up and leave it at your house.

 

[Gebo]

From hence I speak with 100% certainty.

I do no know if it is truly harmful. I do know if you continue to overfill by topping off you may end up smelling gasoline inside a 1998 LS400 for a long time. I started smelling gas. Got a new fuel cap. Looked at getting a new fuel filler neck. Looked at all my emissions stuff. Got worried and worried others.

It really smelled of gasoline when you opened the trunk. And them one day, a backyard mechanic asked me this one question. "Do you keep on topping off your tank after it has clicked off the first time?" I said, "Yes. I fill it up to the top of the neck."
To which he replied, "Stop doing that and come back in a month or two and tell me if you smell any gas. It make take 3 months before the smell goes away."

He was right. I asked him what the deal way. He said I had overfilled it to the point the extra gas had overflowed into my charcoal canister and it took 2 months for the excess to evaporate.

I go now til it "clicks" and stop.

 

[AZjeff]

Originally Posted by y_p_w

However, it's generally not a good idea with modern vapor recovery fuel nozzles with hoods.

No doubt true but not every state has those things. It's an old habit that has the potential to cause some damage and has no real purpose to most.

 

[Rat407]

I round up to the nearest dollar.

On my Cruze diesel, I fill it up until the fuel is level with the opening. Only downfall to that is it takes me a good ten minutes to do so since diesel foams so much. But at least I get an accurate MPG each time.

 

[Bud]

I use to top off when I was younger, but now days when the pump clicks off, I'm done. Still see lots of folks doing it.

 

[2strokeNorthstar]

The recovery nozzles will suck the extra fuel back up if you are full so you are paying for nothing.

 

[Snagglefoot]

Topping off often results in spilled gas. Also it slows sales because some idiot is taking two minutes to buy 10 cents worth of gas. Get in, get out. Move on. There are cars behind you.