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

[brant]

Later when I have time I can find the diagram on this site for fuel routing options

I need to admit that I’m not familiar with routing stock on a six

I know we modified our carbs by drilling percolation holes
This is a common thing done to 911s running carbs
Especially in high heat performance motors


Mine is a measly 2.0/6
I don’t regret any of the things we’ve done to address our fuel system and we don’t have problems despite racing at altitude with less cooling in a dry climate

[Rufus]

@brant Thanks Brant. I’m not trying to be argumentative; only trying to see if there’s something I don’t understand. I understand better now what your suggestions are based on, and whether they might apply to my situation of 100% street driving, using only gas without ethanol, etc., etc..

My thinking is the percentage of excess fuel returned from the OE FP to the tank is warmer than the fuel in the tank at ambient when the engine’s 1st started. How much higher is an open question. But certainly the return fuel is carrying some heat back into the tank and dispersing it into the rest of the fuel in the tank. The longer and harder the engine operates / works, and the lower the fuel volume in the tank, the more the in-tank fuel temp rises. And the more fuel entering the pump and being sent to the carbs heats up.

[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.