Mechanical fuel pump return line

[Logbed]

I'm in a process of swapping the engine. My previous engine and fuel pump did not use the return line. Actually I just found the line was open, sort of a breather for the tanks? Now I could either put a pump without a return and just plug the line, or put a pump with a return and connect it to the line? I just wonder whether the return is leak free? Other potential problems from using the line that I seemingly did not need before. Mechanical pump is the choise but what would you do with the return?

 

[Ricko1966]

Are you sure you have a fuel return line,and you aren't looking at a vent line. If you have a return a 3 port pump with return would be preferable.

 

[Matt69olds]

The return setup would be preferred with today’s lousy gas. The 3 port pumps have a tiny orifice in the return fitting, basically a controlled internal leak. It’s constantly circulating fuel back to the tank which keeps the fuel and pump cool. The other advantage is hot restart. Imagine it’s a 90 degree day, the engine is hot, you have been idling in a parking lot with the A/C going. As hot as it is outside, imagine what it’s like under the hood. Now shut off the engine, imagine how hot it will get after about 20 minutes with zero airflow. Whatever fuel is in the pump and line will begin to boil. The pressure will eventually rise to the point where the fuel pushes the needle off the seat, resulting in a flooded engine. The tiny orifice in the return line provides a vent to bleed off excessive fuel pressure back to the tank making hot restarts much easier.

Since the vast majority of vehicles on the road today are EFI, with closed fuel systems and electric fuel pumps, the oil refineries long ago omitted the additive to prevent fuel boiling and evaporation. We old school carbureted guys make up a tiny percentage of fuel buyers, it’s just not cost effective to include the additive to their recipes.