Refueling Problem

[lyricsdaddy]

Hello all. I have recently bought, say 3 months ago, a 78 GMC C25 pickup. Its got a 5.7 and one gas tank. Since I have bought it, I have been having a refueling problem. I have to pump really slowly, or else the gas overflows and pours out onto the ground. Also, once the tank is "full", it does the same thing. But the gauge never reads full, even pumping really slowly, and it starts to pour out, the gauge only reads between 1/2 and 3/4 full. I have no idea whats wrong, and could use some help. I havent been able to find anything usefull anywhere else, unfortunately. Thanks for all your help! If you need to know anything else about the truck, let me know.

[Greenlee]

It's the the new fancy gas nozzles with the plastic vapor recovery deal. Go out into the country some where they dont have those and it will pump just fine. On my 76' I used to turn the nozzle upside down to get the gas in.
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[79BIG10]

I place the nozzle into the spring and bring back about halfway and turn to left or right. This is the way I've done it and works on the new pumps. Also try filling up slower on the first click.

[Prerunner1982]

I usually never had a problem with it filling up and over flowing. The problem was keeping it from stopping the pump every few seconds. Pulling it out most of the way usually fixed it.

Not sure what is causing it to over flow though....

[lyricsdaddy]

I have tried pulling it out and going slowly, but I still cant get it full. I have not yet tried turning it though... And I just got paid, so I may be doing that tomorrow. Thanks! I didnt know if I had a problem or my truck did. Im not so sure where an "old fashioned" gas station is that isnt 30 cents more per gallon. And Im willing to refuel twice as much than pay that difference.

I actually had the pump stopping problem for about two weeks until I figured out to pull it out. Thanks! It really sucks having to refuel every third day.

[79BIG10]

One more thing is to check the vent lines to make sure they are not clogged. When I worked for F@rd this was a common problem with the trucks that would be getting alot of dirt and dust in it causing the vent not allowing the vapors to come out of the rubber lines.

[lyricsdaddy]

Originally Posted by 79BIG10

One more thing is to check the vent lines to make sure they are not clogged. When I worked for F@rd this was a common problem with the trucks that would be getting alot of dirt and dust in it causing the vent not allowing the vapors to come out of the rubber lines.

Where would I look for these vapor lines? Are they just rubber hoses on the gas tank?

[lyricsdaddy]

UPDATE:

I replaced the vent tube, which was dry rotted so bad it almost wasnt attached. Also made sure that the metal part was free of clogs. I then hit the gas station.

It was slow, but I managed to get about 12 gallons in before the gas came back up the fill hose and splash on the ground. I was at 1/4 tank, now it reads 3/4.

What is the fuel capacity of my tank? Im thinking that maybe the fuel gauge sending unit might be bad, but I have no idea how to test that?

[75ChevyGuy]

I believe I read somewhere that the tanks are roughly 16 gallons.

[mongoose]

shorts are 16, longs are a bit more like 18 or 20.

[Prerunner1982]

Originally Posted by mongoose

shorts are 16, longs are a bit more like 18 or 20.

Longbeds could have had either 16 or 20.

Both my Longbeds had 16s.

[lyricsdaddy]

I did a little research and called my local auto parts store, they said they have a 16 and a 20 gallon tank. I have a long bed, and according to the length of the tank in the truck, it matches the 20 gallon. So, given I was a little above 1/4, and put in 12, thats roughly 18-20 gallons in the tank. So its not a tank-filling issue as I originally thought.

Hmm....

How would I test the gauge and / or the sending unit? Im not real familiar with mechanical fuel pumps and gauges, as everything is electronic now :-/

[Goldfinger]

dont stick it all the way in just put the metal tip in. i use a rag to around it to prevent splash back

[78 Big10 454]

Lyricsdaddy, now you know what I've been putting up with for the past 33 years....

[SoCalKris]

I had the same issue when I got my truck a few months ago,
My trick it to gently shove it in tell it locks in on its own. Then i gently squeeze the handle and latch it on the first notch. Then its just a waiting game. Most times I wont leak a drop, and others it will just be a few drops on the ground