Gas tank problem?

[Tudie 36]

Hello, looking for suggestions. I’ve had The 1936 Tudor about 6 months. It has an after market aluminum tank. Running electric fuel pump and filter at tank, to prime only. I’ve only filled it full maybe twice. I’ve run out of gas about four times. Each time was after short rides, about 4 gallons at fill up was all she would take. Finally realized(slow learner) She would now only take about 4 gallons of gas even bone dry. Twice after about a 30 mile ride gas was pushed out of filler at cap after about 5 minutes of parking. Any ideas before I drop the tank? I’m going to run a wire down vent tube tomorrow, the wife’s flower wire was too dainty. Help

[Willit Stop]

Wrong gas cap? It should be vented.

[Tudie 36]

Originally Posted by Willit Stop

Wrong gas cap? It should be vented.

That was my first thought, emailed supplier before ordering a replacement. The one on it now if Ford scripted locking cap. Doesn’t appear to be vented to me. The supplier told me they consider locking caps as vented. ???? I believe the event tube in the top of the filler neck travels to just short distance. So would a vented or non vented be required? Still don’t understand why it would stop accepting fuel. I wish I was smarter

[40cpe]

Maybe pick up tube doesn't go to bottom of tank. '36 has a sending unit? If so, take it out and inspect tank through hole.

[Dick]

I agree with Willit Stop. Without the vent a vacuum is created that the fuel pump can't overcome.
I had it happen to me on my F-1 and the vented cap cured the problem.

[Flathead Fever]

Sponsored Links (Register now to hide all advertisements)

Thiis is a weird one. If the cap was not vented, while driving it would create a vacuum inside the tank and not a pressure. As the fuel is sucked out by the pump air has to be able to enter the tank through the caps' vent to replace the fuel being taken out. If the air cannot enter the tank it will build up a vacuum. And eventually the vacuum in the tank will be equal to the fuel pumps vacuum and the fuel cannot move.

How can it be running out of gas, bone dry empty and then running out of the filler after the fuel sits and expands, and supposedly were only dealing with four gallons in the tank. I can understand running out of gas with only four gallons but not running out of the filler. What does the gas gauge say when its supposedly full? There are contradicting things going on here that do not make since at all. Check to make sure the exhaust is not heating the fuel in the tank and expanding it, that could explain it running out of the filler but not why you can only get four gallons in the tank. It just seems to me like you have multiple problems going on. The gas gauge can't possibly be working or you would not be running out of gas.

Why would four gallons of gas be all that will fit in that tank? That is weird! Was the manufacturers' shop cat a sleep inside the bottom half of the tank when they welded the top half on? Is four gallons all that will go in until the gas pump nozzle clicks off or is four gallons all that goes in until the tank is full to the top? Some tank designs are a pain in the butt to fill without pressure developing in the tank and causing the gas pumps' nozzle to continually click off. We had certain trucks at work that did that. On those I stuck an ink pin between the nozzle seal and the filler neck so it would not build up pressure.

Modern caps "non-vented" caps are still "vented" caps. The difference is they have an inlet valve that opens to let air flow into the tank when it starts to develop a vacuum as the fuel is removed and they have a pressure relief valve that will open if the gas expands on a hot day and creates too much pressure in the tank. The expanding fuel could be forced out into the EVAP charcoal canister and saturate it. Under normal operation these valves are closed which prevents the hydrocarbons from escaping into the atmosphere. Old gas caps like the ones on Early Fords and Mustangs just have a little vent hole in them sometimes its hidden in the caps construction and hard to see. True non-vented caps are usually heavy brass caps with a thick gasket. They come from the 1910s brass era when you needed a sealed system and a handpump so you could build up pressure in the tank and push the fuel to the carb. You closed a valve, and pumped up the pressure, and then continued to give the handpump a stroke every once in a while. Then when you stopped you opened the vent valve and released the pressure so the carb couldn't possibly flood over.

Jack Calori, that had a record setting flathead dry lakes roadster in 1947, which he also drove on the street with only hand pressure pump. Used a very old, teen era brass Cadillac gas cap to seal the tank. He told me that on a hot day, with a full tank, the fuel would expand enough to create its own pressure in the tank, and you didn't need to pump the hand pump at all, until the fuel level started to drop. Then you needed to give it a little pump everyonce in a while to keep the pressure up on the gauge.

[Terry,OH]

The locking gas caps, if reproductions, are vented. If original there is a screw to remove for the vent. The screw is marked "vent" and stamped into the plate next to the screw. The original 36 filler neck has a J-shaped vent tube in the filler neck at the cap connection. The neck vent should allow the tank to be filled properly.
The 35-36 restoration book sold by the V8 Club has good photos of the filler neck and vent.

[TJ]

Double check the filter and the electric pump to make sure they flow in the correct direction. Both filter and pump are marked with an arrow to show the flow direction. The arrow on both should be pointing towards the motor. If the car has a custom made tank there may be some problem with the tank itself. I've never heard of a gas tank in any old Ford to only hold 4 gallons.

[waterboychuck]

Back in the 60's I was driving a Ford Van for work and someone stole the gas cap and the dealer replaced it. A short time later I was sitting at a traffic light and when it it turned green I stepped on the gas pedal and the van acted like it ran out of gas even though the gauge said I had plenty. A tow truck came and haul the van back to the dealer. They admitted as to putting on a non vented cap and had to replace that but also had to install a new tank as it imploded. You may want to remove your tank, or if if can see it clearly, to see if that has happened to you.

[Tudie 36]

Originally Posted by Terry,OH

The locking gasB99FCA61-D9D4-475B-A852-8C712154EEA1.jpg

3F4197EB-5CAE-4676-8EAF-E8BBB9FFC3C9.jpg

EC409056-D20C-4110-BA18-C570E2EDF9C1.jpg

0FC7A78E-2C93-4815-8984-26FE1DDD51DF.jpg caps if reproduction are vented. If original there is a screw to remove for the vent. The screw is marked "vent" and stamped into the plate next to the screw. The original 36 filler neck has a J-shaped vent tube in the filler neck at the cap connection. The neck vent should allow the tank to be filled properly.
The 35-36 restoration book sold by the V8 Club has good photos of the filler neck and vent.

Thanks for the replies, sorry for late response. Decided to give it a break and Crappie fish today. Here is what I have. I have 4 screws but not a vent stamp. My gas gauge doesn’t work. I have put 10-14 gallons in her previously. Pump and filter is pointed the right direction. We disconnected from carb and run electric pump to view gas for residue. Ran a siphon in tank looking for anything in the bottom, clean.

[Terry,OH]

You have an early reproduction locking gas cap which I suspect is vented. You also have the 36 style of filler neck vent which I would suspect is blocked. It is difficult to see if blocked when mounted on the car since the tube makes a J-bent at the cap end. I think there is a special cap on the vent tube at the gas cap end.

[fordyford]

I have had original tanks that developed a rust pin hole in the pick up "straw". You could only drive until the level of gas dropped below the pin hole
(4 gallons) and the pump could only draw in air.

Is it possible your reproduction tank has a pin hole or crack in the fuel pick-up?

[Tudie 36]

Originally Posted by fordyford

I have had original tanks that developed a rust pin hole in the pick up "straw". You could only drive until the level of gas dropped below the pin hole
(4 gallons) and the pump could only draw in air.

Is it possible your reproduction tank has a pin hole or crack in the fuel pick-up?

I do think so but I’m going to find the right size wire and push through the J tube. It has just started doing this. So the repo. cap won’t need a screw removed to be vented? And if so, wonder which one?

[Tudie 36]

Originally Posted by Terry,OH

You have an early reproduction locking gas cap which I suspect is vented. You also have the 36 style of filler neck vent which I would suspect is blocked. It is difficult to see if blocked when mounted on the car since the tube makes a J-bent at the cap end. I think there is a special cap on the vent tube at the gas cap end.

Thanks, I’ll try to push a wire through. And see what happens

[fordyford]

I do not think that you have a plugged vent. Try driving with the cap removed.

The reason the car stops after using only 3 gallons is not explained by a plugged vent. If that was the problem you would hear a rush of air entering the tank when you removed the cap and the car could then be started and driven another 3 gallons.

I still think you have a crack or pin hole in the tube that sucks gas out of the bottom. When the car dies, do you still have about 7 gallons in the tank?

[J Franklin]

That tank didn't happen to come up from Mexico? Maybe there is something someone forgot to remove!

[VeryTangled]

Not sure I love this idea but might it be time to see if the fuel tank drain is working and see how much comes out.

[Tudie 36]

I’m out of town for a few days, will post what I find. Dang Gremlins

[Tudie 36]

Originally Posted by J Franklin

That tank didn't happen to come up from Mexico? Maybe there is something someone forgot to remove!

HaHa I’ll look