21 gallons in my gas tank?

[AirSpeed]

A few days ago I filled up the tank in my 72 GMC K1500, my gauge read about 1/8th of a tank. I let it fill up by itself and when done I noticed I had just bought 21.2 gallons. Is this possible? I thought my tank only held 17 gallons and have never got 21 gallons in it! I usually don't let it get below 1/4 tank so I can't remember how much it's held before. The worst part is the price of gas dropped .50 a gallon the next day!
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[Stocker]

It's possible, but you were running on fumes. With 3 tanks, I have put that much in my in-cab tank, though I don't recall the exact amount. I do remember taking just over 50 gallons to fill up once -- ouch.

[SS Tim]

Well maybe.... the nominal capacity of the '72 half tons is listed as 20 gal. This is down from the 21 gal of the heavier and all earlier trucks without EEC. Is your evap sysem functioning properly?

[AirSpeed]

Originally Posted by SS Tim

Well maybe.... the nominal capacity of the '72 half tons is listed as 20 gal. This is down from the 21 gal of the heavier and all earlier trucks without EEC. Is your evap sysem functioning properly?

I've never noticed any issues other than a very slight gas smell the day I fill the tank, that goes away overnight. I always thought the stock tank was 17 gallons for some reason. Could a faulty vent system account for extra fuel capacity?
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[SS Tim]

That is kind of what I was wondering. Need to dig through my stuff and take a look.

[Stocker]

Originally Posted by AirSpeed

I always thought the stock tank was 17 gallons for some reason.

Seems like there was a discussion about that but I can't find it.... IIRC, some trucks had a standard 17 gallon tank with an optional 20 or 21 gallon tank. Other trucks came with the larger tank standard.

At least that's what my not-so-great memory is telling me.

[cdowns]

a faulty vent system will not allow for gallons upon gallons of excess gas capacity/// unless you left a very large puddle of callons upon gallons of gas on the ground


me i dont ever trust a gas gauge and one of the first things i will do with an old vehicle is to run it out of gas so i know the exact spot that the gauge reads when i should worry (when doing it i do carry a 5gallon can of gas with me)

[special-K]

All pickup gas tanks are the same size,no optional tank offered. They hold 21 gallons. It is possible to squeeze just a bit more,but nothing unusual about your tank. I have had trucks with a fuel gauge and speedometer not working that took just shy of 21 gallons and was very happy I decided to go ahead and stop for fuel.

[SS Tim]

Originally Posted by cdowns

a faulty vent system will not allow for gallons upon gallons of excess gas capacity/// unless you left a very large puddle of callons upon gallons of gas on the ground


me i dont ever trust a gas gauge and one of the first things i will do with an old vehicle is to run it out of gas so i know the exact spot that the gauge reads when i should worry (when doing it i do carry a 5gallon can of gas with me)

Right, we were talking about the approximate 1 gal difference between the EEC and non-EEC trucks.
There is no way the system could likely allow even a gallon to be stored in the lines. So if there is more than a normal amount in the tank something would have to change in the EEC capture and venting to allow the extra usable capacity within the tank.
As I understand it the fuel level is reduced by extending the filler neck a little deeper to create an air pocket at the top of the tank. Then it is this pocket in conjunction with a non-vented cap that collects the vapors which are routed to the canister and ultimately the engine.

BTW... Running a vehicle dry to see where the gauge "reads" is still "trusting" a potentially faulty gauge if you use that as a future reference.

[special-K]

Yeah,I learned a long time ago to trust no gauge past 1/4 tank. Besides,even if it reads accurate down to "E",fill-ups are a lot cheaper! LOL Most of these trucks I've had,the gauge doesn't move for the first 1/4 tank. Then,it drops faster the lower it gets.

['68OrangeSunshine]

I have found that I could cram 22.5 gallons into the in-cab tank on my '68 C/10. That's with fuel dripping out the spout [even with the cap on] on right turns. Don't fill it up-to-the-neck high on a cool night and then park in the sun the next morning. Don't park with the passenger side higher than the driver's side.

[long67]

My book lists tanks in 67 as 18.5 with a 20.5 optional tank. I always thought mine was 15 gal, guess cause it emptied so fast.

[twouvakind]

There are reported inaccuracies at the pump and inspectors do uncover them, just a thought.