Underhood fuel line routing help

[JeepSnake]

Doug,

Actually, the long return line acting like a radiator has little to do with the way the return style system works to keep the fuel cool. The circulation is what's important.

Think about a regular old carbureted fuel system: no regulators, no return. Just a fuel pump, a line, and a carb. Unless the engine is really loaded and consuming a lot of fuel, there is a bunch of fuel sitting static in the fuel line. As it sits there, the fuel line absorbs heat from the engine & headers and transfers it to the fuel. This can wind up resulting in vapor lock.

So, to solve this problem, you add a return line near the carb, and you put in a higher volume fuel pump. Now, the pump is always moving fuel through the fuel line, even when the engine isn't loaded, and returning it to the fuel tank. This cures the heating/vapor lock issue in two ways: 1) the moving fuel doesn't have as much time to pick up heat as it passes through the engine compartment fuel lines, and 2) what heat it does pick up is dispersed into the heat sink of 20+ gallons of fuel in the tank. As a friend put it to me, you keep the fuel moving and it doesn't have time to just hang out and get in trouble.

In the '70s, as engine operating temps increased, this system was incorporated into production cars to fight vapor lock. I know that Jeeps used a fuel filter just ahead of the carb with two outlets. One fed the carb, the other returned fuel to the tank so that you didn't vapor lock while creeping offroad.

Hope this helps.