1957 Vented or not vented gas cap

[TbirdFan76]

Should the gas cap be vented or not? The one that came with mine is not vented.

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[Tom Alpers]

Should the gas cap be vented or not? The one that came with mine is not vented.

Must be vented. If your trips are short a non-vented may work but on longer drive a vacuum will build making it much harder to pump fuel. Todays "vented" caps have a more restrictive vent than in the old days plus they don't like to let pressure out... at some level of pressure build up they will vent. I had a new one on mine and did not like how much pressure it would let build up. I was afraid it might force fuel past the pump and flood the carb but not aware of that actually happening. I drilled a small hole in the new cap to make it fully vented. The downside to that the vent hole may let gas spill out when its full on a curve.

 

[ICON 56]

If the gas cap is NOT vented then, Your car will have vapor lock and will stall.

 

[TbirdFan76]

Adding some photos. I've seen the same cap on ebay being sold as an original 57 tbird part.

Unless the venting is happening beneath the rubber seal I don't see any place for air or fumes to pass.

 

[SHA BOP]

Must be vented. If your trips are short a non-vented may work but on longer drive a vacuum will build making it much harder to pump fuel. Todays "vented" caps have a more restrictive vent than in the old days plus they don't like to let pressure out... at some level of pressure build up they will vent. I had a new one on mine and did not like how much pressure it would let build up. I was afraid it might force fuel past the pump and flood the carb but not aware of that actually happening. I drilled a small hole in the new cap to make it fully vented. The downside to that the vent hole may let gas spill out when its full on a curve.

My 55 has the original style gas cap and no problems since 1987 with no vent holes drilled. You mention a vacuum will build and you also mention pressure build up. I don't believe pressure will build up but I can understand a vacuum may occur due to a full tank of gas being used creating a vacuum in place of used gas. I keep the gas tank fill tube and the gas cap cleaned and lubed. Seems to work as designed by Ford, for me. Thank you for great inputs.

 

[Tom Alpers]

My 55 has the original style gas cap and no problems since 1987 with no vent holes drilled. You mention a vacuum will build and you also mention pressure build up. I don't believe pressure will build up but I can understand a vacuum may occur due to a full tank of gas being used creating a vacuum in place of used gas. I keep the gas tank fill tube and the gas cap cleaned and lubed. Seems to work as designed by Ford, for me. Thank you for great inputs.

Have you ever gone for a drive, the pulled into a gas station to get gas and when you turned the cap heard a whoose of "air" going in or out? If not, something might be venting your tank. The pressure I was talking about was due to how they make modern vented gas caps. They have a one way valve in them, they will let outside air go into the tank but will not let gas fumes vent back out which causes pressure to build up inside the tank. The old gas caps would let air go in or out thru a pinhole.

 

[SHA BOP]

Tom, thank you for your reply. May I ask, if pressure builds up in the tank, there will not ever be a vapor lock. As you indicated earlier, a vacuum can create a vapor lock.
To answer your question, I have never had the whoose air noise but that is due to the fact that my fuel cap is operating as designed. I agree that if your fuel cap is not functioning properly and allows a vacuum to build in the tank, it can cause fuel starvation. The small hole in the cap is a solution. Safe journeys

 

[Tom Alpers]

Tom, thank you for your reply. May I ask, if pressure builds up in the tank, there will not ever be a vapor lock. As you indicated earlier, a vacuum can create a vapor lock.
To answer your question, I have never had the whoose air noise but that is due to the fact that my fuel cap is operating as designed. I agree that if your fuel cap is not functioning properly and allows a vacuum to build in the tank, it can cause fuel starvation. The small hole in the cap is a solution. Safe journeys

If pressure built would that prevent vapor lock... Good question. I don't know because I don't know if the valves in the fuel pump would act as a gate keeper and keep that extra pressure from getting past the fuel pump and into the fuel line that goes from the pump to the carb. My concern, which I had no way to verify, was that the pressure build up would force fuel thru the fuel pump when the car was shut off and would cause flooding and fuel dilution of the oil. Didn't want to risk that experiment so went back to an old fashioned cap that vents both ways.

 

[SHA BOP]

Please tell me how and what can cause pressure to build in the fuel tank. Pressure in the tank would tend to force fuel to the carb but cannot cause a vapor lock. A vacuum is created (if fuel cap does not vent properly) when a full fuel tank is used creating a low pressure area / vacuum / and vapor lock will stop fuel flow to the carb.
I am second owner of my 55 bird and never had a problem (purchased in 1987) and never experienced any vapor lock issues. But, I believe my fuel cap functions as designed. If I had vapor lock issues and new fuel cap did not resolve the problem, I would certainly consider drilling a tiny hole in the cap.

 

[Tom Alpers]

Fill the tank when it's 60 degrees, put a non-vented cap on it, park it in the sun. You will find you have a pressurized gas tank. If you don't, it's venting to somewhere. Similarly, fill it in mid afternoon then let it cool overnight. It will have a vacuum in the morning if cap is not vented. I have had gas shoot out of filled up gas tanks from pressure build up. I don't think anyone is saying this issue is necessarily related to vapor lock issues.

 

[TbirdFan76]

Have you ever gone for a drive, the pulled into a gas station to get gas and when you turned the cap heard a whoose of "air" going in or out? If not, something might be venting your tank. The pressure I was talking about was due to how they make modern vented gas caps. They have a one way valve in them, they will let outside air go into the tank but will not let gas fumes vent back out which causes pressure to build up inside the tank. The old gas caps would let air go in or out thru a pinhole.

@Tom Alpers I've not experienced the whooshing noise at fill up. My question has to do with an issue I had last week on my way to a car meet.

The day was 90 degrees and I was caught in road construction barely moving for about 20 minutes. Needless to say the 57 Tbird temperature got hot - above 230. It died twice while stuck in traffic on the highway. After returning home and turning the engine off I had significant gas leaks from the carburetor that didn't exist beforehand. My thought was that high pressure created in the fuel system due to gas liquid turning to vapor in the metal lines near the engine. I drained fuel from this lines and carburetor to release any pressure that may stiil be in them.

Long story but I was also concerned that the gas cap may be a contributing factor.

 

[Tom Alpers]

@Tom Alpers I've not experienced the whooshing noise at fill up. My question has to do with an issue I had last week on my way to a car meet.

The day was 90 degrees and I was caught in road construction barely moving for about 20 minutes. Needless to say the 57 Tbird temperature got hot - above 230. It died twice while stuck in traffic on the highway. After returning home and turning the engine off I had significant gas leaks from the carburetor that didn't exist beforehand. My thought was that high pressure created in the fuel system due to gas liquid turning to vapor in the metal lines near the engine. I drained fuel from this lines and carburetor to release any pressure that may stiil be in them.

Long story but I was also concerned that the gas cap may be a contributing factor.

Do you have a typical Holley carb on it? They have a vent on the top of the front fuel bowl as well as an internal vent. There is no way for any pressure to build up inside the carburetor aside from the fuel pressure against the needle and seat. To pressurize the internals of the carb it would have to fill the fuel bowl above the normal level set by the needle and seat. If you don't have a vented gas cap and the whole system is building up pressure from the heat and then you shut it off so no more fuel is being consumed maybe it's possible there is enough pressure to force fuel past the fuel pump and past the needle and seat and flood the carburetor that way. That could force fuel out of the vents and perhaps bleed fuel over into other passages. Curious as to how you know what the temperature was... do you have an aftermarket temperature gauge with actual numbers on the dial? Do you still have the factory gauge? What kind of reading do you get on it?

 

[TbirdFan76]

Do you have a typical Holley carb on it? They have a vent on the top of the front fuel bowl as well as an internal vent. There is no way for any pressure to build up inside the carburetor aside from the fuel pressure against the needle and seat. To pressurize the internals of the carb it would have to fill the fuel bowl above the normal level set by the needle and seat. If you don't have a vented gas cap and the whole system is building up pressure from the heat and then you shut it off so no more fuel is being consumed maybe it's possible there is enough pressure to force fuel past the fuel pump and past the needle and seat and flood the carburetor that way. That could force fuel out of the vents and perhaps bleed fuel over into other passages. Curious as to how you know what the temperature was... do you have an aftermarket temperature gauge with actual numbers on the dial? Do you still have the factory gauge? What kind of reading do you get on it?

Yes, the car has an aftermarket temperature gauge. The original in the dash is not functioning.

Yes, the carburetor is a Holley List 1273-1 that is original to the car. I rebuilt it with a kit from Allstate Carburetor. Also rebuilt the fuel pump with a kit from Hills Thunderbird.

 

[Tom Alpers]

What have you done to get better cooling? It should not/need not run that hot even under those conditions.

 

[Lionel]

Our 57 has a vent tube in the filler tube and a sealed cap exactly as in the picture. Get under your car at the rear just in front of the filler you should see the vent. It’s probably blocked with mud. Fuel vapour lock is possible if you don’t have an isolating gasket under the carburettor. I fitted modified inlet manifold gaskets from CASCO they have smaller exhaust equaliser holes which reduces the heat underneath carburettor heating chamber.

 

[George Ford]

I had an issue with my 55 puking fuel when the cap was removed the generic cap that apparently had the one way valve. I replaced it with a 55 cap that vents in and out problem resolved. I recall while researching the issue that later models had a vent tube so yours could be blocked.

 

[TbirdFan76]

Our 57 has a vent tube in the filler tube and a sealed cap exactly as in the picture. Get under your car at the rear just in front of the filler you should see the vent. It’s probably blocked with mud. Fuel vapour lock is possible if you don’t have an isolating gasket under the carburettor. I fitted modified inlet manifold gaskets from CASCO they have smaller exhaust equaliser holes which reduces the heat underneath carburettor heating chamber.

Is this the vent you're referring to? This photo is taken looking down the fuel filter tube.

 

[Tom Alpers]

Our 57 has a vent tube in the filler tube and a sealed cap exactly as in the picture. Get under your car at the rear just in front of the filler you should see the vent. It’s probably blocked with mud. Fuel vapour lock is possible if you don’t have an isolating gasket under the carburettor. I fitted modified inlet manifold gaskets from CASCO they have smaller exhaust equaliser holes which reduces the heat underneath carburettor heating chamber.

If your car is configured as when it left the factory that is not a "vent" in the sense we have been discussing here, which is a vent to atmosphere. That vent tube is an internal vent to allow the gas tank style used in the 57's to fill completely. Without it there would be an air bubble at the top of the tank preventing it from filling completely. That vent vents that air/fumes that collect at the top of the tank to vent out to the filler tube while you are putting gas in. While filling up it is, of course, venting to atmosphere because the gas cap is off. As soon as you put a non-vented gas cap on you would have completely closed it off as far as venting to atmosphere.
Your mention of it does raise an interesting thought however. That vent tube is two parts... the part on the filler tube, and a second part on the gas tank. The two parts are joined by a short piece of rubber hose. Given how old these cars are it is possible the rubber hose is cracked or shrunk and not making a good seal anymore. If that were the case you would get a bit of a gas leak or seepage thru the cracked or shrunken hose and you would also get an atmospheric vent even if you did use a non-vented gas cap.

 

[TbirdFan76]

If your car is configured as when it left the factory that is not a "vent" in the sense we have been discussing here, which is a vent to atmosphere. That vent tube is an internal vent to allow the gas tank style used in the 57's to fill completely. Without it there would be an air bubble at the top of the tank preventing it from filling completely. That vent vents that air/fumes that collect at the top of the tank to vent out to the filler tube while you are putting gas in. While filling up it is, of course, venting to atmosphere because the gas cap is off. As soon as you put a non-vented gas cap on you would have completely closed it off as far as venting to atmosphere.
Your mention of it does raise an interesting thought however. That vent tube is two parts... the part on the filler tube, and a second part on the gas tank. The two parts are joined by a short piece of rubber hose. Given how old these cars are it is possible the rubber hose is cracked or shrunk and not making a good seal anymore. If that were the case you would get a bit of a gas leak or seepage thru the cracked or shrunken hose and you would also get an atmospheric vent even if you did use a non-vented gas cap.

Is the vent on the tank only visible from the top? Where would I look?

 

[SHA BOP]

Tom, good information. My 55 does not have that vent tube in the fill tube photo. In the old days, they did not use the rubber seal around the fueling nozzle like they do today, so there was plenty of room for venting the fuel tube to atmosphere.
This is an interesting discussion, I have never experienced a vapor lock issue in my 55 over the 38 years I owned my bird. It is a very clean 2nd owner car that is close to factory delivered. It worked when it was delivered but over the 70 years, things change and many birds go through mods that often cause more modifications.