Fuel disappearing

[Zymurgy]

Also there is a gasket between the filler neck and the tank, that go bad and a royal pain to change, but you will have all the telltale signs of leaking fuel that we have mentioned.

 

[Big_John]

There's a locking cap on it already? You don't smell or see gas either?

Let's regroup here....

You are noticing gas loss... are you seeing this in the gauge? If so, you really might not be accurately measuring the loss.

The gauge is 45 or so years old... and it runs off an ancient 5 volt regulator. It measures resistance from the tank sender using electricity to heat a bimetallic strip that moves the needle. Not real accurate to begin with and none of the components exactly age like fine wine.

You fill the tank, the sender has less resistance, the gauge heats up and the needle moves up. You drive around a bit, the sender goes down, the gauge cools off a little and the needle moves down.

You shut the car off, the needle goes to zero and cools off.

Start the car up, the gauge warms up again and starts to move the needle up... Now something called "hysteresis" comes into play. The needle movement is from a different direction and the it's a little worn.. so it doesn't come up as high. The gauge doesn't heat up as fast or as much either. The voltage regulator is a little stiff and there's some gas condensate on the tank sender that's increasing resistance.

So... the gauge doesn't read as high as it did when you parked the car. All the things that affect accuracy are coming into play now and the gas gauge does not read the same as it did when you parked it, even though the gas level is the same.

In other words, it's just the gauge.

 

[josehf34]

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.)

Every day I've to drive on hills, In my fury the gas filler is not behind the license plate but is very close to that location, but I have never noticed any gas smell when driving. I'm start by fixing or replacing the gas cap tomorrow

There's a locking cap on it already? You don't smell or see gas either?

Let's regroup here....

You are noticing gas loss... are you seeing this in the gauge? If so, you really might not be accurately measuring the loss.

The gauge is 45 or so years old... and it runs off an ancient 5 volt regulator. It measures resistance from the tank sender using electricity to heat a bimetallic strip that moves the needle. Not real accurate to begin with and none of the components exactly age like fine wine.

You fill the tank, the sender has less resistance, the gauge heats up and the needle moves up. You drive around a bit, the sender goes down, the gauge cools off a little and the needle moves down.

You shut the car off, the needle goes to zero and cools off.

Start the car up, the gauge warms up again and starts to move the needle up... Now something called "hysteresis" comes into play. The needle movement is from a different direction and the it's a little worn.. so it doesn't come up as high. The gauge doesn't heat up as fast or as much either. The voltage regulator is a little stiff and there's some gas condensate on the tank sender that's increasing resistance.

So... the gauge doesn't read as high as it did when you parked the car. All the things that affect accuracy are coming into play now and the gas gauge does not read the same as it did when you parked it, even though the gas level is the same.

In other words, it's just the gauge.

A worn gas gauge could be another possibility, I think I'm going to fill the car tomorrow and let's see how much gas will it drink. But, if the gas gauge is worn, maybe the fuel reading would be higher sometimes and that's not happening

 

[josehf34]

I just filled up the car, I was hoping that maybe this all was about a bad sending unit or bad gas gauge but in total I put 22 gallons in tank , so 22 gallons "disappeared" in something like 80miles that about 3.5 mpg I don't know what's going on with all this situation, I don't know if has something to do but I've noticed that always when I filled up there's still 5 - 6 gallons remaining in tank.

My car originaly came with vapor canister but I unpluged the lines, can be possible to have a leak at that point?

Tomorrow I'm going to run the car with a bottle of 2 gallons and see what happens if it last more than 7 miles I think is just enough to consider I've a leak in some place

 

[Zymurgy]

Wow sorry to hear this. I saw there was a new post had hoped you had found the problem. Your plan seems like a good place to start. Never really hear anyone getting much below 7-8mpg. Good luck.

 

[Snotty]

My car has had a leak. I never had to worry what or where because a) I could smell gas every day as soon as I entered my garage, and b) I could see a stain on my garage floor.

At one time (on another car) I had a leak on the fuel pump. Again, there was a smell and the pump was very clean where there was oil and grime everywhere else on the motor.

I had a leaky fuel line going into the carb. There was a heavy smell of gas every time I drove it, and I could see signs of the leak on my intake.

What you are describing is an incredible loss of fuel. If there were a leak - anywhere - your nose would know it before any other sign could be seen. And a sign would be there - somewhere! I still think you're being robbed.