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Gas Tank (run dry)
So tonight I managed to legitimately run out of fuel. Hasn't ever happened to me before. Got her filled up and she started like a snap. Curious thing though. What is the capacity of the original tank? I barely got 15.5 gallons in before I was topped off. But I could swear that I had seen that it was a 20 gallon tank.
Now if I have 5 gallons worth the gunk in the bottom of the tank, you wouldn't know it from seeing through the sending unit hole where the tank looks nice and clean. Is there a clogged air escape valve that is prohibiting me from filling the whole way?
Also, its a big no no to run the tank dry on an old car. I have rebuilt carbs before and rebuilt this one too, but I'd like to avoid it. Should I run it for a few more miles and change the filter? As I said, no issues starting and driving the last 10 miles home.
Thanks for any suggestions.

Looks like there is a fuel tank vent line on the top somewhere? I imagine I will have to drop the tank to get to this.
they claim the tanks are 20 gallon for normal and 22 gallon for a premium version. I've never tested a tank to see what it holds from dry i always had something in the tank. 15 gallons would make sense when my gauge reads 1/2 empty i've always assumed my gauge was off based on 22 gallons. maybe the volume of the tank could in theory hold 20-22 gallons but the pop off for the fuel pumps only allow 15 gallons max or maybe the way the filler neck enters the tank prevents the extra 5 gallons.

i would love to know what others think.
The funny part is, in an attempt to get it as full as possible, I fill the fuel up until I can see the gas in the filler pipe (and then I let it go down lol). But it seems odd that there is 5 gallons I can't use. I bought a replacement tank from CJ Pony parts awhile ago and it is listed as a 20Gallon tank. Now Im concerned maybe my car is some fluke and that new tank won't fit.
I've never let mine run empty, the most I've put into at once was a littel over 17 gallons.


M code 71 Mach 1, 351 4V Cleveland, Ram Air (not factory), C6 Trans, 3.5 rear
another thing is if the replacement tanks are larger then the original tanks, then there would be a problem with the metal straps that hold the tank to the underside of the trunk floor. or you would have an exhaust clearance issue with the stock tail pipes or hangers.

i know its impossible to fill one of these tanks to 100% capacity first it would come out the filler neck and the Fuel vapor vent on top of the tanks. i also know that one time when i replaced the sender i siphoned out the tank, and thought it was empty popped the ring seal and got at least 1 gallon of gas in the face. somebody told me the tank is designed to not show an extra gallon when you get to E on the gauge as some kind of fail safe against you running out of gas but i think that is an old urban myth. the sender never really gets 100% to the bottom of the tank so i would imagine there is quite a bit of gas that you can never truly use when the car says you are empty.

i think ill start treating my tank as only 15 gallons and see what happens.
Let me throw a off kilter point of veiw. Are you sure it was empty or just stopped picking the fuel up at that level?
Tnfastbk;80658 Wrote:Let me throw a off kilter point of veiw. Are you sure it was empty or just stopped picking the fuel up at that level?

ding, ding ding!!! we have a winner!

I am pretty sure all 71-73's originally came with the 20 gallon tank and there was not a 15 gallon tank for them. Maybe a early model tank could have been utilized but I doubt it.

[Image: 1_01_07_15_8_53_18.png]

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!
so 40 years ago ford lied. 20 gallon tank with a 15 gallon usable capacity Big Grin
improper pick up placement due to improper sending unit orientation?

[Image: 1_01_07_15_8_53_18.png]

"I love my Hookers!" and "Get some Strange" probably have a different connotation to non automotive enthusiasts!
The owners manual on my 73 states 19.5 U.S. Gallons. Only taking 15 gallons is odd. Was your car level on on a slope when you ran out of gas or filled it up?

Mike AKA Ole Pony & Rare Pony

Our current Mustang garage/driveway
1973 Mustang Convert - Bought in 1974 - Still have it!
2004 Mach 1 Oxford White Auto, Bought Sept 06

[Image: 20180127_082009.jpg]

upload a photo on internet

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