Fuel disappearing

[josehf34]

Hey guys

I have something like a weird fuel problem with my '74 Fury. According to owners manuel the gas tank capacity of this car is about 27 gallons and I always fill it up

The problem is that I think the fuel is disappearing, all fuels in my country has between 10% - 15% ethanol content which is something like 4 gallons of ethanol per each full gas tank (27 gallons) so is normal that sometimes some of that ethanol evaporates. The deal here is that If I left the car sitting in the garage I can see the fuel gauge come down 1/8 per each 3 - 4 days, that is about loosing 4 gallons of gas each 5 days that the car is sitting

I don't know if I'm a bit confused or what's going on here. I've checked for fuel leaks in garage floor or trying to find any weat fuel line but everything seems to be fine, the unique strange issue that I've noticed is that sometimes after driving the car I can see the gas in fuel filter boiling but I don't know if is really boiling because I don't feel it boiling inside the carb

The gasket on my fuel cap is gone, can this be causing this problem?

What else can I check?

 

[300rag]

Are you actually losing fuel, or is the sending unit not floating as is should, and slowly sinking, giving those readings? I suspect that the sending unit is your problem.

 

[josehf34]

Are you actually losing fuel, or is the sending unit not floating as is should, and slowly sinking, giving those readings? I suspect that the sending unit is your problem.

The sending unit is new and the reading never fluctuates, if I fill the car again it will go up to "full" and will start coming down. In less than one month without using the car more than 100 miles I can see the gauge near the "half" mark

For example the last time I filled it up was like 5 weeks ago, and since then I've drove like 50 miles and have the car sitting due to a cylinder head job, and now I've like 3/8 of tank

 

[Snotty]

A gas leak will leave a sign - somewhere. Are there spots under your car where you park it? Gas will evaporate but I doubt, very seriously, at the rate you are describing.

Where do you park it? Is it secure? Is there a possibility that someone is siphoning your gas? do you have a roommate that needs gas too?

Unrelated, but 27 gallons? I thought the largest tank used on Mopar passenger cars was 24?

 

[Big_John]

I had the same issue with my company car. The fuel level would go down for no mechanical reason, especially if the car sat for more than a day or two.

The solution was, quite simply, a locking gas cap.

Bet someone is getting in and siphoning gas.

I figured with my car that they were only taking a gallon or two at a time. I might not have noticed except the car would occasionally not get driven for a week or so... and the gas level would go down a lot more.

 

[josehf34]

A gas leak will leave a sign - somewhere. Are there spots under your car where you park it? Gas will evaporate but I doubt, very seriously, at the rate you are describing.

Where do you park it? Is it secure? Is there a possibility that someone is siphoning your gas? do you have a roommate that needs gas too?

Unrelated, but 27 gallons? I thought the largest tank used on Mopar passenger cars was 24?

According to owners manual the '74 fury gas tank is a 100 liters unit and 100 liters is like 26.5 US gallons (100/3.78)

I don't have roommates or something like that but my garage is shared with the neighbors I don't know if somebody could be stealing me gas, I think is a close possibility

I had the same issue with my company car. The fuel level would go down for no mechanical reason, especially if the car sat for more than a day or two.

The solution was, quite simply, a locking gas cap.

Bet someone is getting in and siphoning gas.

I figured with my car that they were only taking a gallon or two at a time. I might not have noticed except the car would occasionally not get driven for a week or so... and the gas level would go down a lot more.

How did you figure how much gas was being stolen?

 

[Big_John]

I don't have roommates or something like that but my garage is shared with the neighbors I don't know if somebody could be stealing me gas, I think is a close possibility

It doesn't mean that it's your neighbors. But it does mean that it is accessible by others. Mention it to your neighbors... Just ask if they've had problems and see if it stops.

You could put a piece of thread across the license plate and see if it's broken the next time... A trail camera is $50 (or maybe can be borrowed from a hunting buddy) to catch the culprit.

 

[jct]

my dad had the same problem with his truck until he bought a locking gas cap. he found out it was the neighbors kids taking it (couple houses down)

 

[josehf34]

Let's assume that somebody is stealing my gas. What are the most common ways of siphoning gas from one of these old cars? I mean, the gas tank and fuel lines of modern cars are a lot complex than in old cars, maybe there's an easy "back door" on old cars that I can fix

Does a locking gas cap has any special security feature? I mean, I've been googling it and it looks like a normal cap with lock and my car have one of these since I bought it

 

[68Nwprt]

Make sure the cap is in the locked position. Can you remove the cap without using the key?

 

[Big_John]

The time honored method just involves a hose, a can and a mouthful of gas if you aren't careful. The old cars are pretty easy... Stick the hose in the filler and suck on the hose to get the gas flowing and then stick the hose in the can.

These days, there are siphon hoses available with a squeeze bulb that primes the siphon hose and takes the challenge out of it.

 

[300rag]

...
Does a locking gas cap has any special security feature? ...

I chuckled at that. When I got my wagon, it had a locking cap with only one key. I went to the locksmith to see if he had a blank that would work. After searching for a while, he found one and wanted to make sure it fit the keyway before he cut it. It fit like a glove, and also opened the cap uncut. I guess any key that fit would open it.

 

[Zymurgy]

I believe the stealing gas theory. I had a gas leaking problem in the past and when you would open the garage door the fumes would knock you over, and it wasn't even close to the amount of fuel you are losing, and you would never loose that much from evaporation around the cap.

 

[300rag]

If someone is stealing it in those amounts, maybe it's going into a motorcycle.

 

[Zymurgy]

If someone is stealing it in those amounts, maybe it's going into a motorcycle.

Sounds like a neighbor kid, they only put in what they need and hoping they won't get caught. A stranger would just empty the tank and be gone.

 

[Snotty]

These days, there are siphon hoses available with a squeeze bulb that primes the siphon hose and takes the challenge out of it.

Yep, I have one of those and getting gas out of my Newport is very easy!

 

[josehf34]

Make sure the cap is in the locked position. Can you remove the cap without using the key?

The cap feel like isn't completely locked but I can't remove it without key

The time honored method just involves a hose, a can and a mouthful of gas if you aren't careful. The old cars are pretty easy... Stick the hose in the filler and suck on the hose to get the gas flowing and then stick the hose in the can.

These days, there are siphon hoses available with a squeeze bulb that primes the siphon hose and takes the challenge out of it.

I chuckled at that. When I got my wagon, it had a locking cap with only one key. I went to the locksmith to see if he had a blank that would work. After searching for a while, he found one and wanted to make sure it fit the keyway before he cut it. It fit like a glove, and also opened the cap uncut. I guess any key that fit would open it.

But that method needs to have the cap removed, I'm not sure if somebody can have enough time to remove it with a blank key (I have to try if I can remove it with other key) with the building security staff hanging around

I believe the stealing gas theory. I had a gas leaking problem in the past and when you would open the garage door the fumes would knock you over, and it wasn't even close to the amount of fuel you are losing, and you would never loose that much from evaporation around the cap.

If the gas cap gasket is gone can be possible to have the gas leaking through the cap for example going uphill?

 

[70bigblockdodge]

I had a gas disappearing problem, found out it was proportional to my right foot movements.

 

[Snotty]

If the gas cap gasket is gone can be possible to have the gas leaking through the cap for example going uphill?

Yes. Have you been driving up hills on a regular basis? However, if this is true there will be tell-tell signs under your car and on the filler tube. Gas always leaves stains. If it's running out while going up hill there will be drip deposits and other signs.

Not only going up hills, but every time you leave from a red light gas would leak out the back. (I am making a HUGE assumption that your filler tube is behind the rear license plate. If it's above on the side, all of my comments are moot.)

 

[Zymurgy]

Buy a new cap they are cheap. When my old cap was leaking I could smell the fuel from inside the car while driving.