1970 -6 Gas Tank Supply Pipe Hose Bead Question, Morphed into: “Does the OE fuel return system cool fuel going to engine?” uh … No Options

[Rufus]

Hi Folks - I have the entire fuel system out of 9140431482 back to the Webers for update, cleaning, etc. (Webers already reinstalled after thorough cleaning.) The gas tank fuel outlet pipe has no hose bead.

Is this normal? Seems odd there wouldn’t be one.

Thanks,
Bob

[Rufus]

I referred to AutoAtlanta’s part system views & descriptions for fuel system plumbing info. The OE -4 and -6 systems at least through ‘74 appear to be the same wrt returning fuel from the pump to the tank and excluding engine compartment lines and carbs from the return circuit.

So even if a return system included the engine compartment lines and carb float bowls, the return system would cool fuel going to the engine. But only until fuel in the tank is warmed to the point where the fuel temp exiting the pump exceeds that of a returnless system under the same conditions.

Returnless system allows the tank fuel to remain at ambient temp no matter how long or hard the car’s driven or how low the fuel drops. 100% of the fuel flow between the tank and pump is consumed in the engine. The pump should run hotter in this case where there’s no cooling provided by excess fuel returning from the pump to the tank .

OE type system w/ Return - If the car’s run long & hard enough with the tank volume dropping, the heated tank fuel going to the pump will cause the pump’s output fuel temp to rise, eventually reaching and surpassing that with a returnless system.

If I had to guess, I’d say the return was to forestall pump vapor lock to more extreme operating conditions of longer, harder driving combined with a dropping fuel tank level. Was a great help wrt vapor lock back in the days before the introduction of ethanol blended gas.