Gas Tank Issue - Vintage Mustang Forums
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post #1 of 15 (permalink) Old 08-22-2019, 11:35 PM Thread Starter
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Gas Tank Issue

Hello guys,

I am having an issue with what I thinking may be a gas tank issue. During restoration the car sat for some time and not all the gas was drained from the tank. It is the original 16 gallon tank.

The issue I am having is when filling the car up it only lets me pump about 6 to 7 gallons then the pump stops. After getting gas and looking at the gauge it only goes to 3 quarters full. When the car runs out of gas the gauge stops at a quarter before empty.

I was thinking of getting a new tank kit with a new sending unit but thought it would be a good idea to see what you guys think and if anyone else has experienced this.


Thanks in advance.

64.5 Mustang Coupe, 302 V8
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post #2 of 15 (permalink) Old 08-23-2019, 04:53 AM
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It sounds like 1) you have a big dent or something in the tank that is taking up a bunch of its capacity and 2) your sending unit is possibly screwed up from 3) sitting for a long time with a partial tank, especially modern fuel with ethanol in it, causes rust and corrosion in the tank.
I highly recommend you or your favorite mechanic drain the tank (should be a 3/8 square plug on one corner of bottom), open the sending unit lock ring (faces rear axle), remove the sending unit and have a look around inside with a GoPro or mobile phone camera (be CAREFUL with fuel vapor...may be wash the tank out with water first). Maybe it's time for a new tank and a new sending unit.

My 1st car...
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•LOTS of Rotunda accessories

Older son's 1st car...
'66 Emberglo / Parchment deluxe coupe
•289 / 2100 •C4 Auto
•Dealer A/C • Console
•Dual Exhaust • Power Steering

Younger son's 1st car...
'66 Nightmist / Blue & white deluxe coupe
•289 / 2100 •C4 Auto
•Factory A/C •Console
WAITING FOR RESTORATION

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post #3 of 15 (permalink) Old 08-23-2019, 08:49 AM
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If you're not as motivated as myfirstcar66 you can pull the filler hose off of the tank in the trunk and shine a flashlight in there and get an idea if it's rusty or not. You can even shove a little camera in there if you've got one and you don't have to drain the tank or anything. If it looks nasty in there you'll know you need to order a tank.

Still, don't start any fires or breathe too many fumes or anything like that. Well ventilated area, etc etc.

If the tank's not rusty or dented the problem is probably just your sending unit. You can try and clean it or you can replace it (search around here, there are plenty of sending unit threads) but of course that's going to take draining the tank.

Before you start breathing all the gas fumes though make sure it's not the gauge. It's probably not, but it doesn't cost anything to check. While you're under the car looking for dents pull the wire off of the fuel tank sending unit and ground it to a clean spot on the body somewhere. Then go turn the key to 'Run' or 'Accessory'. The gauge should go all the way to full. If it does (and it probably will) you know the issue is with the sending unit. If it doesn't, definitely fix the gauge first since that doesn't involve dropping dirt, rust and gasoline in your face and all that.
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post #4 of 15 (permalink) Old 08-23-2019, 09:25 AM
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For the cost of a brand new tank with sender through NPD- why even mess with it?
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post #5 of 15 (permalink) Old 08-23-2019, 10:18 AM
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Basics

Forgive me if you know all this, but how do you know the tank is full when pumping gas and how do you know it is empty ?

I ask this because old cars will usually stop more than once on a fill. Then you start again (maybe a little slower) and fit in more. With my new(er) cars, I pull the pump handle all the way; 1st stop, it's done.

With my 67, it is a juggle of the right amount of gas to not shut off the pump too early yet not spending 10 mins filling. And it shuts off at least twice before it is really full.
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post #6 of 15 (permalink) Old 08-23-2019, 11:26 AM
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Because the tank is not vented, as the gas fills and sloshes up, there's nowhere for the air to go and the safety on the pump handle sense the fuel, shuts it off.

My 1st car...
'66 Tahoe Turquoise/ Aqua coupe
•289 / 4100 •C4 Auto •Disc Brakes
•Dual Exhaust •Quick Manual Steering
•Rally Pac •Console •Deluxe Belts
•LOTS of Rotunda accessories

Older son's 1st car...
'66 Emberglo / Parchment deluxe coupe
•289 / 2100 •C4 Auto
•Dealer A/C • Console
•Dual Exhaust • Power Steering

Younger son's 1st car...
'66 Nightmist / Blue & white deluxe coupe
•289 / 2100 •C4 Auto
•Factory A/C •Console
WAITING FOR RESTORATION

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post #7 of 15 (permalink) Old 08-23-2019, 08:18 PM Thread Starter
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Thank you all. I will check the gauge like mentioned by @Magnus. I inspected the tank and there are no dents.

64.5 Mustang Coupe, 302 V8
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post #8 of 15 (permalink) Old 08-23-2019, 08:53 PM
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How long was the car sitting...?....If it was anymore than 3 years...The tank is trash. Pony up for a new tank and a new sender..

The reason is that the Ethanol Gas will trash the tank....The inside of your tank will look and have the consistency of burnt Caramel.

Cars that are constantly driven will not have an issue...but will require more frequent fuel line changes and more frequent carb rebuilds..

It's the demon of driving E10 Ethanol Gas. (Thanks Obama)....

)

Tony K.
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Tony Kovar
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Last edited by NEFaurora; 08-23-2019 at 08:57 PM.
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post #9 of 15 (permalink) Old 08-23-2019, 11:04 PM
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Also, do whatever you can to SAVE that old sending unit, if it's not rusty... A deft hand can get a look see at the rheostat to see if it can be cleaned and then test it. The originals are non-linear, unlike the replacements, which means that the windings match the profile of the tank... a half-full tank ISN'T when the level of fuel is halfway to the bottom because the back of the tank is sloped... it's just more accurate than the new ones.
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post #10 of 15 (permalink) Old 08-24-2019, 10:46 PM Thread Starter
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@ NEFaurora The car sat for about 10 years. I think I am just going to go with a new tank kit.

I appreciate all the info guys.
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64.5 Mustang Coupe, 302 V8
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post #11 of 15 (permalink) Old 08-24-2019, 10:53 PM
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And while you're at it, protect your investment by using non-ethanol / pure gas . It's out there, costs a little more but it has more stores energy than ethanol/gasoline so you'll get better mileage, more power, easier starts, corrosion and condensation in the fuel system won't be nearly the issue.

My 1st car...
'66 Tahoe Turquoise/ Aqua coupe
•289 / 4100 •C4 Auto •Disc Brakes
•Dual Exhaust •Quick Manual Steering
•Rally Pac •Console •Deluxe Belts
•LOTS of Rotunda accessories

Older son's 1st car...
'66 Emberglo / Parchment deluxe coupe
•289 / 2100 •C4 Auto
•Dealer A/C • Console
•Dual Exhaust • Power Steering

Younger son's 1st car...
'66 Nightmist / Blue & white deluxe coupe
•289 / 2100 •C4 Auto
•Factory A/C •Console
WAITING FOR RESTORATION

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post #12 of 15 (permalink) Old 08-25-2019, 01:50 AM
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"The car sat for about 10 years. "

Oh, Yeah. That tank and sender are toast....fer sure. No question.


There was an article about rescuing old tanks years ago (without re-coating the insides like using an Eastwood's Tank kit which is an entirely different approach) and then I actually saw it mentioned on an episode of Fantomworks of all places......Something about filling the tank half way with Acetone and flipping over the tank every 6 months for a 1 year to 1 1/2 period. The Acetone dissolves all of the Burnt Carmel old Gas....something like that...to that effect..

)

Tony K.



Tony Kovar
Melbourne, FL (Formerly from Long Island, NY!)

1965 Mustang Convertible 200cid I6, 3spd Manual (Soon to be swapped for a '65 Date Coded C4!)
1966 Mustang Sprint 200 Registry Owner/Moderator
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post #13 of 15 (permalink) Old 08-25-2019, 10:13 AM
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^^^ wow. Tony's absolutely right. That might be okay for some one-of-one, a really rare car with no reproduction tank but we in this hobby enjoy quality reproduction tanks that are very affordable... heck somebody will give you a decent used one... you can even get stainless steel and reproduce the original US Steel or Ford markings. Definitely worth that.

Last edited by myfirstcar66; 08-25-2019 at 10:18 AM.
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post #14 of 15 (permalink) Old 08-25-2019, 11:29 AM
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Plus, while you're at it....you could go with a bigger tank form a 67-70 mustang if you wanted farther range for trips or less frequent fill-ups!
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post #15 of 15 (permalink) Old 08-25-2019, 12:07 PM
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If you tank doesn't have a drain plug, I would disconnect the fuel line at the carb and pump the fuel into a container by running the car from a portable fuel container. Once the tank is drained, I would run a couple of gallons of fresh fuel to help clear the fuel lines. If you are considering a new tank and sending unit, I would definitely pick up a couple of new fuel filters.
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