gas tank and gauge - strange situation

[RonnyB]

Hi folks - new member here. Not sure what's up with the Dart, but I've wondered for years.

My shop manual says the gas tank is either 18 or 19 gallons. Got gas yesterday, and the gauge read about 1/8 of a tank. Filled it up, but it only took 9.7 gallons.
The previous fillup was four days before. Gas mileage was normal for the car: just over 15. Modified Slant 6/auto trans.

My question is, why does it normally take only 10-12 gal when the gauge reads almost empty? It's been that way for many years. I only get about 150-170 miles per tank. This car rarely gets driven, and that's one reason. In the last seven years, it's only been driven 4,000 miles.

I keep gas and mileage records in a little book, and since 2005 the most I've been able to get in the tank is 12.7 gallons. I had thought maybe it was evaporating or had a really small tank, but took the factoy service manual to the doctor's office this week and was surprised at the size tank it's supposed to have. I think this last tank lasting only a few days rules out evaporation. Maybe somebody put some inflated beach balls in it way back when...=P~

The sending unit's float sprang a leak a couple years ago and was replace, but didn't change the situation. The voltage regulator stuck several years ago and fried the gas and temp gauges. Replacing them also didn't change anything. So I'm really confused about what's going on. I'm tempted to carry a gas can and just let it run out of gas one day when I'm not in a hurry to get where I'm going, just to see if the gauge is accurate. Other than that, I don't know how to diagnose this problem.

It's no fun having to get gas every 170 miles or so, 'specially when it comes gushing out the filler neck almost every time... uke:

So I appeal to you, A-body experts! What's going on with my little Dart? Thanks!

 

[7demon2]

what year car? the first thing that comes to mind for me is the fuel pickup and sending unit is sitting to high off the bottom of the tank. it would read empty if it is too high off the bottom and therefore you would not need that much gas to refill it....

 

[7demon2]

just saw that you have a 64 from your signature. if this is the right year you should have an 18 gal tank according to the hamtramck data page for your car....http://www.hamtramck-historical.com...ook/1964/64_Dodge_Index_Secifications0006.jpg

 

[RonnyB]

...the first thing that comes to mind for me is the fuel pickup and sending unit is sitting to high off the bottom of the tank. it would read empty if it is too high off the bottom and therefore you would not need that much gas to refill it....

I wouldn't bet the farm on it, but I'm pretty sure this was happening before the sending unit was replaced.
I've still got the old one here. Yeah, I know: 'What kind of person keeps a busted sending unit around for years?':wack:

It looks like it's possible that it could be in there crooked (causing the float to go up and down at an angle), but then it wouldn't read full when the tank is full. Also, there are two metal tabs coming out from the 'mounting plate' that are slightly offset to one side. That would only allow it to go in one way. I suppose the replacement could have been missing them (?), but that would have caused the hose connection to be coming out at a different angle than before, and again, it wouldn't read full with a full tank.
I'm going to jack the car up and see if I can see the sending unit on the tank. Just to see if the gas outlet is pointing straight up like it should.
I didn't replace it myself, but my mechanic is very competent and it's pretty safe to assume he put it in correctly.

Here's a shot of the old sending unit. See how those mounting/guide tabs are slightly off to one side?

Pretty strange problem, isn't it? It's had me puzzled for several years...

 

[7demon2]

yeah i know what you are saying, but if that fuel pickup tube (second arrow on right bottom) is not down far enough in the tank it will be too high and sitting above the fuel in the bottom of the tank.....it would read empty and still have gas left..

 

[VDART]

Does it have the original gas tank in it? I believe the 62 valiant tank only held 14 gallons & could be swapped into your vehicle. Ma mopar cleaning out old stock put it in place of your 18 gallon 1. Just fuel for thought, Lawrence

 

[BrianT]

... but if that fuel pickup tube (second arrow on right bottom) is not down far enough in the tank it will be too high and sitting above the fuel in the bottom of the tank.....it would read empty and still have gas left..

Sorry but the pickup level has nothing to do with what the gas gauge reads. The float arm may have gotten bent on installation. Or the float itself may have a hole in it. If the float is setting too low in the tank, that could be why it reads 1/8 tank when there is a half tank of gas.

 

[bigdemo1]

Not to jack but my 77 truck does this sort of,says 5/8 full after filling,when it's on empty it's still got 3/8 tank,bad float thats all.

 

[RonnyB]

Does it have the original gas tank in it? I believe the 62 valiant tank only held 14 gallons & could be swapped into your vehicle. Ma mopar cleaning out old stock put it in place of your 18 gallon 1. Just fuel for thought, Lawrence

As Artie Johnson used to say, that's very interesting! I got it in '99 and don't know any history of it before that other than it was in Los Angeles when I bought it. But I checked my log book and in Nov 2000 we put 15.53 gallons in it. Hmmm.

The float arm may have gotten bent on installation. Or the float itself may have a hole in it. If the float is setting too low in the tank, that could be why it reads 1/8 tank when there is a half tank of gas.

I thought about that. When I fill the tank, the needle is just barely touching the full mark. Should it be reading past the full mark? I know some cars will peg the gauge after a fillup.

How likely is it that I got a sending unit that has the wrong resistance? I can't find a receipt for when it was changed, bit I think this was happening before then. Unfortunately, I can't be sure without a dated receipt.

One thought I had was to see if I could see how much gas there is by feeling the side of the tank, but I really can't tell.
Could this be the excuse I need to finally spring for one of those cool infrared thermometers? =P~

 

[cudajim]

If it were my car I would yank the sending unit out and see if it works the gauge properly by moving the float up and down. You'd have to jack up the car and have the gas gauge wire hooked up as well as a ground. Most likely all you have to do is bend the float a bit so it does not bottom out too early.