1957 6237SDX fuel tank vent tube

[Bob Pawluk]

57 and 58 Eldorado's have a second connection on the fuel tank filler vent tube. What is it for? What is it connected to?

[Mike Baillargeon #15848]

The fuel tank should have an air vent on the upper side of that tank....your smaller tube connects to that with a rubber hose....

Fuel goes into the tank and air in the tank goes back up into the top of the fuel fill pipe....

Mike

[Bob Pawluk]

If you will look at the picture you'll see two connections on the vent tube. The question is what is the small second vent connection for on Eldorado's only?

[Lexi]

I am not 100%, but the small tube may be a return line that originally ran from the engine's fuel filter on AC equipped cars, back to the fuel tank. The tubing that it connects to is as Mike described, (a vent stack). So 2 different jobs being done here. Clay/Lexi

Edit: Found this older CLC Forum link where this matter is discussed. Have a look.
https://forums.cadillaclasalleclub.org/index.php?topic=127285.0

[Bob Pawluk]

Thanks but ac cars have a hard return line that runs along side the fuel line.    The small rubber line in question is on Eldorado's only

[Mike Baillargeon #15848]

Thanks but ac cars have a hard return line that runs along side the fuel line.    The small rubber line in question is on Eldorado's only

I'm stumped...somebody hopefully will have a picture of their 1957 Eldorado on a lift.....

I think I pulled this fuel filler pipe from a 57 Seville years ago....it has 3 small tubes coming off of the fuel filler tube !

There is nothing in the 1957 shop manual about these lines and in the 1958 shop supplement manual there is mention of the AC return line....

It wouldn't surprise me that these vents just allowed excess fuel to spill on the ground if there was any kind of expansion in the tank rather than pour out of the fill cap....

Mike

[fishnjim]

I doubt they'd just dump fuel as that presents a definite fire hazard and once it starts it could syphon.
I'd go the other way as it's a high point vent, they connected more things from the rear, but have no idea what those are other than guesses.   air suspension, differential, etc.
I'd block it off, if nothing to attach.

[Lexi]

Like Mike I am also stumped. I don't know where the fuel return line attaches at the tank, though Bob says it does not connect at the vent stack. That said, I wonder if the return line was vented, and if so could the connection in question be a vent for the return system if so equipped? Let us know when you find out. As Jim suggested it seems to be a high point vent of some sort. Clay/Lexi

[J. Gomez]

Mike,

There is a possibility the fuel filler tube on your picture was used on cars with non-vented fuel tanks with an atmospheric vent valves and return lines thus the three tubes.    

Bob,

As for your topic the extra "T" line if not for A/C return line it maybe for the added atmospheric vent valve on non-vented fuel tanks.   

On the late '56-37SDX and 67SX they used the vented valve on the filler tube so there is a possibility the same arrangement was used on the '57-'58 when they start adding the extra return line. 

If you look at the MPL there are several filler tubes listed for all the '57 and '58 so finding a correct answer would be a tough task unless owners for each of the specifics models validates them.