I have a 71 Chevelle SS 454 and there is an original 20gal gas tank on it. But, I've run it to empty where the car shuts off (gas gauge doesn't work) and when I filled it up it only took around 9.5gallons. Could there really be 10gal in the floater which could be bad or
does that not make much sense? Any ideas?

My 72 held much less than the factory specs called for. It had a huge dent in it which took up fuel space. I replaced the fuel tank and now it holds closer to 19 gallons or so.
Also, some of the newer gas pumps will shut off when the back pressure hits them. I had to slowly put gas in after it got over 1/2 a tank.

My guess would be the pump is shutting off prematurely. Not sure if the 72 is the same as the 69 which has the filler tube behind the license plate but when I add more fuel after the pump clicks off you can see the fuel rise up the filler tube. Next time you go to fill up take a gas can with you. After the pump clicks off put a few gallons in the can. If the Chevelle takes the additional gas you will know there is probably room for another ten gallons after the initial click off. If it won't take the gas you will know something is wrong inside your tank and you can add the rest of the gas from the can later.

I have a 2gal can in my trunk in case I run out since the gas gauge doesn't work but I'm not understanding what you are saying really? Is there something inside the tank that can close off to make the fuel fill up faster or not let in as much gas when adding?

Smuggling drugs in the gas tank? l:)

On my '69 I have to put the nozzle on the slowest setting when filling otherwise it will splash back and shut the pump off... even put a new tank in it, and it still does the same thing.

Being that you are dealing with a 1972 Chevelle which is 36 years old at present a lot of things could have transpired before you took possession of the vehicle. Maybe a previous owner placed some substance inside the tank which takes up half the volume or it could have some type of obstruction in the filler neck which would not allow fuel in as rapidly as it should. There shouldn't be anything inside the tank that would interfere with putting all 20 gallons in. But if you say you only able to put ten gallons in from the point of being empty filling it up with ten gallons and then trying to add more fuel via the fuel can you will be able to tell if it is really full when the pump shuts off at ten gallons. Unless gas is spilling out the filler neck at 10.5 gallons then the tank isn't really full when the pump clicks off.

Maybe there is 10 gallons left in it & the pickup is broke of or incorrect?

LK

Drop the tank, pull the sending unit and take a look. Guessing at what the problem might be will never solve the problem. Might be a good opportunity to fix your gas gauge problem at the same time.

And maybe locate a build sheet!!!! :)

How is the set up of the car?
Does it sit stock level?
Raised in rear
Slightly lower in rear will make the what other here have said much worse
My 68 had a plugged tank vent causing the early cut off problem


maybe Pubishers Clearing House hid your 10 million $$$$$$ cash prize in your tank
NOT l:)

Maybe there is 10 gallons left in it & the pickup is broke of or incorrect?
LK

Like mine? Some had jacked it up by the tank before I got it, but the fuel weight must have pushed it bak closer to normal.
http://i168.photobucket.com/albums/u165/Bowtie-Bry/TECH/BentLine.jpg

Drop the tank, pull the sending unit and take a look. Guessing at what the problem might be will never solve the problem. Might be a good opportunity to fix your gas gauge problem at the same time.

That's half of what I did too.


And maybe locate a build sheet!!!!

:yes: I did!

http://i168.photobucket.com/albums/u165/Bowtie-Bry/TECH/DSC03245.jpg

Looks like Team Chevelle was watching over me last spring.....

How is the set up of the car?
Does it sit stock level?
Raised in rear
Slightly lower in rear will make the what other here have said much worse
My 68 had a plugged tank vent causing the early cut off problem


maybe Pubishers Clearing House hid your 10 million $$$$$$ cash prize in your tank
NOT l:)

Are you sure? 20 years ago I was driving mine back and forth from MD to NC going to college. I would load the Chevelle down to the point where the headlights were shooting high ito the air. I never had a fuel problem.

On mine when I fill it I can tell when it is getting full. The tank gives a slight "pop", the nozzle will shut off, you wait a second and 2 more gallons will go in. The car has done this since it was new.

Not sure if the 72 is the same as the 69 which has the filler tube behind the license plate but when I add more fuel after the pump clicks off you can see the fuel rise up the filler tube.

Most of our gas tank filler tubes are behind the license plate, which is different than most if not all cars today. Some people have trouble occasionally with gas coming out on hard acceleration or on a hill with the car facing backward. So when is it full? When it's at the bottom of the filler neck, or when the gas starts to just drip out of the filler neck?

I have been asked in the past to fix some gas tanks that were dented in the center of the tank.I used air pressure to blow the dent back out with the gas tank still on the car.Most of these tanks showed no outside damage afterwards.The sending units were damaged on most of these cars,like Bowtie 72's picture, but the owners of the cars did not want to replace the sending units

Is 20 gal. the standard size? My '71 Malibu seems to hold exactly 15 and I thought this was normal.

Would sure love a few extra gallons in there, but shame as I just dropped the tank last month to replace the sender - and things seemed fine...

:yes: I did!

http://i168.photobucket.com/albums/u165/Bowtie-Bry/TECH/DSC03245.jpg

Looks like Team Chevelle was watching over me last spring.....

Sure is a good feeling....that's for sure!!!

http://i51.photobucket.com/albums/f382/M60-E4/1971%20Chevelle%20SS/IMG_1088.jpg

Maybe there is 10 gallons left in it & the pickup is broke of or incorrect?

LK
this is whats taking place!

Either your car has a secert hidden Drug smugling compartment in the gas tank ie: only ten gallon cap. or your gas cap is bad and your running untill you collaspe the tank and fuel pump cant draw fuel anymore and when you remove cap an gas up you release the tank to atmosphere pressure again and fill up your missing fuel and over and over, try removing the gas cap and see if car runs again. Otherwise follow advice from previous members.

Douglas
Sir!!!!! would you please step out of your vehicle a strange odor our dogs picked up on is being release from you car. And check the ground wire, may have been left off on purpose IE: the smuglers,,.... Good Luck

See if you can find a set of old "Chevelle Reports" There is a GM TSB on these tanks. It describes where the filler did not get placed through the bracing at the inside top of the tank and the result was the filler being low in the tank.
That would contribute to a low tank fuel level.

tachman here:
check the resistance on the tank sending unit with a vom, empty is 2 ohms, full is 90 ohms. check for grounds
www.tachman.com/gm.htm
need help toll free 1 800 327 8716 m-f 9-6 est
tachman

See if you can find a set of old "Chevelle Reports" There is a GM TSB on these tanks. It describes where the filler did not get placed through the bracing at the inside top of the tank and the result was the filler being low in the tank.
That would contribute to a low tank fuel level.

Ah - that's sounds likely. Anyone have a source for this report? Thanks...

Sure is a good feeling....that's for sure!!!

http://i51.photobucket.com/albums/f382/M60-E4/1971%20Chevelle%20SS/IMG_1088.jpg

Thats where I found mine too

How is the set up of the car?
Does it sit stock level?
Raised in rear
Slightly lower in rear will make the what other here have said much worse
My 68 had a plugged tank vent causing the early cut off problem


maybe Pubishers Clearing House hid your 10 million $$$$$$ cash prize in your tank
NOT l:)
Yeah the rear is lifted a little because of the drag shocks. I am going to put on street shocks in the spring and at same time probably drop the tank and see whats going on. thanks everyone for all your help!