This is proly a stupid question but how does the gas pump no when to turn off when the car is full? I've always wondered.

The back pressure of the gasoline trying to go back into the handle (nozzle) is what shuts it off.

This may help.

When your gas gauge reads empty, your tank is filled with air instead of fuel. As you add fuel, the air must move out of the tank to make way for the gas. Next time you fill your car at the gas station, take a look at the pump nozzle. You will find a hole about a half inch from the end of the nozzle. This hole is connected to a small pipe that travels through the nozzle to the handle.

When you fill your gas tank, some of the displaced air flows through the hole in the nozzle into the pipe. When the tank is full, the hole will be below the gasoline level and no air will pass through the pipe. A mechanical switch inside the nozzle detects when the flow of air stops and shuts off the gas.

You may have noticed that, after the pump shuts off, you can get more gas in your tank by pulling the nozzle out of the tank a bit. This is because you’re moving the position of the hole relative to the gas level and allowing the mechanical switch to reopen.



Does this help at all, LOL

That just about sums it up nicely. Geez and I was going to respond to this one, but figured the "pros" would understand the science behind the pumpage of gas!

Good summary!

1990 is close.

That small hole 1990 discussed actually is a venturi creating suction. When the tank is not full, air is being drawn through the hole by the vacuum, and the air flows easily. When gas in the tank rises high enough to block the hole, a mechanical linkage in the handle senses the change in suction and flips the nozzle off.

the info I got was from one of the websites I searched for. It came directly from a company ( that deals with them).

I never said I was an expert, LOL
just know how to search.

I had researched it a while ago (year or so) while I was bored.

I always thought that the gas pump was shut off by the same little man who turns the light off when you close the door on the fridge. Hmmmmmmm. For me, the reason why the gas pump shuts off is because it realizes that there is no more money on the credit card I put in there to pay.

heheheh kinda like the little guy in ricers when they overheat they open the trunk and the lil man screams "Ahhhh hh I told you not to run it so hot" hehehe

JUNKMAN strikes RICERS again lol

BONNES RULE RICERS JUST DONT

OK.. Where'* the overfill gas valve located? I've been told that when it stops.. that'* it.. you're tank is full.. and when people always try to narrow it to the closest dollar ( duh.. that'* why you pay with debit and plastic ) they are actually supposedly just wastin money and fuel. I heard this from one of them car shows 2 years ago.. is this valid ?