1957 Vented or not vented gas cap | Page 2 | Ford Thunderbird club group 1955-2005 T-Bird models

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1957 Vented or not vented gas cap

  • Thread starter Thread starter TbirdFan76
  • Start date Start date
SHA BOP said:
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.
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The 55 and 56 did not have the vent tube, they didn't need it because the filler neck went into the tank at an angle at the top and there was no place for an air bubble to form. The 57 filler as at the side of the tank and a little bit below the top so it needs the vent to make full use of the tank capacity.

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Cars of this period had filler caps that were vented to the atmosphere. Without that vent, the mechanical fuel [ump cannot draw correctly as there is no incoming air pressure (atmosphere) to allow the gasoline to be drawn out easily. It can result in the car cutting out (incl blend separation before the pump if ethanol laced) or the extreme, a collapsed fuel tank. The tank will build pressure in a heated environment (think sunshine and/or heated garage) and has to be vented to expel the pressure.

The fuel bowl vent(s) are only there to expel pressure from the bowl after shutdown (heat soak expansion) and not the main vent to prevent hard re-starting. While driving, the bowl(s) are vented through the main vent(s).

The tank venting is different on each year BIRD.

CAP ASSY (9030) - FUEL FILLER - 1949-1959 FORD CAR TXT.pdf.png​
 
It seems that pressure and vacuum are being described as the same issue. Pressure that builds in the tank cannot collapse the tank. However, vacuum could, in theory, collapse the tank. Pressure in the tank would not prevent fuel flow as pressure in the tank will increase fuel pressure to the pump. However, vacuum will stop fuel flow causing vapor lock. Thank you for your information regarding venting. Like you stated, the fuel caps for the 55 / 56 allows pressure to vent out of the tank and atmosphere to vent into the tank to prevent vacuum building.
 
Tom Alpers said:
It starts at the top and goes around to where the filler neck goes in. If you are under the car it's easy to see. In the photo you can see the parts and how they connect with the rubber tubing.
View attachment 34088
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The pictures help alot. Per your notes it looks like the fuel filler vent connects to the tank vent. If the tank vent and filler tube vent connect and the gas cap isn't vented how is pressure released to the atmosphere? Is that a small hole for venting to atmosphere at top of the tank (new tank photo)near the hole for the filler tube?
 
KULTULZ said:
Cars of this period had filler caps that were vented to the atmosphere. Without that vent, the mechanical fuel [ump cannot draw correctly as there is no incoming air pressure (atmosphere) to allow the gasoline to be drawn out easily. It can result in the car cutting out (incl blend separation before the pump if ethanol laced) or the extreme, a collapsed fuel tank. The tank will build pressure in a heated environment (think sunshine and/or heated garage) and has to be vented to expel the pressure.

The fuel bowl vent(s) are only there to expel pressure from the bowl after shutdown (heat soak expansion) and not the main vent to prevent hard re-starting. While driving, the bowl(s) are vented through the main vent(s).

The tank venting is different on each year BIRD.

Click to expand...
What do the letters in column 2 mean or do they not matter? Is column 3 what's important relating to the gas cap vent?
 
TbirdFan76 said:
The pictures help alot. Per your notes it looks like the fuel filler vent connects to the tank vent. If the tank vent and filler tube vent connect and the gas cap isn't vented how is pressure released to the atmosphere? Is that a small hole for venting to atmosphere at top of the tank (new tank photo)near the hole for the filler tube?
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Yes, those vent tubes don't vent to atmosphere except when the gas cap is off. That is why you have to have a vented cap to avoid building up a vacuum (or pressure).
 
Tom Alpers said:
Yes, those vent tubes don't vent to atmosphere except when the gas cap is off. That is why you have to have a vented cap to avoid building up a vacuum (or pressure).
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Ok, back on your August 14th post you said "The old gas caps would let air go in or out thru a pinhole." Looking at my 3rd picture from August 12th zoomed in it looks like there may be pinhole sized holes. I'll check the gas cap again with a magnifying glass and another photo for pinhole sized openings.
 
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