Hey guys, when does the return line perform its duty? Is there constant fuel being returned to the tank or during specific times only and is it under pressure?

JR

Fuel is returning all the time the pump is running. In theory, there is no return pressure, but in reality there is a slight pressure due to minor resistance to flow, but VERY slight.

A percentage of fuel returns to the tank at all times.  This helps keep fuel from being heated in the lines by allowing constant flow.  Not heating the fuel from engine heat helps prevent vapor lock.

In fuel injected cars the return does the same thing, and helps the pressure regulator maintain a constant pressure to the injectors, or in the case of port fuel, a variable fuel pressure.  In either case, still no return pressure.

Thanks for the detailed explanation, Ken.....I guess there would have to be enough pressure to make the uphill climb back into the tank. BTW, this on a '72.

JR

[QUOTE=daveb12]OK, then how come my 68 big block doesn't have one?[/QUOTE]

i think they added it in 69 to prevent vapor lock