Fuel Return Line?

TerryR · Saturday at 8:48 PM

I posted this in the JD Owning and Operating forum and got over 500 views but no responses. I'm re-posting it here in hopes of catching the eye of someone who understands what fuel return lines are about.

On the top of the engine on my JD 870 are three serpentine hoses that connect to the fuel injectors. From the parts diagram I gather the are part of the fuel return system. What does the fuel return system do? Why does fuel have to be returned?

The hoses in question are item #10 on this diagram:

The reason for asking is that one of them was chewed by mice years ago, and I replaced it with a hose from the auto parts store. Fifteen years later it's leaking again, so I just replaced it and think I fixed it.

joecdeere · Saturday at 9:05 PM

to keep it overly simple, injection pumps always pump more fuel than is consumed by the injectors, this helps keep the injectors from lacking the fuel needed with a sudden change in RPM's, also keeps the system full and air out. So in the end, the extra unneeded fuel travels back to the tank or to the fuel filter housing (depending on model and brand) to begin the trip again. Again, this is over simplified, but hopefully answers your question.

Tinhack · Saturday at 9:26 PM

Simple fix for a simple problem. Those lines are typically not under a lot of pressure. On my Ford, the return line also provides fuel for the cold weather pre-heater.

TerryR · Sunday at 9:15 AM

Thanks, joecdeere. I didn't understand what it was for, and that explains it.

I had trouble finding the issue because I found fluid on the floor under it when parked, but only sometimes. I finally saw the leak when it was running, and replaced the hose. Then I figured out why it was occasional. The top of the fuel tank is higher than the leaky hose, so it only leaked while parked when the tank was full.

dodge man · Sunday at 9:18 AM

A good question and I didn’t have an answer.

mini14 · Sunday at 10:16 AM

the returned fuel also acts like a coolant as well and the warm returned fuel helps in the winter to warm the fuel in the tank. If the machine is operated for a long time it also polish's the remaining fuel in the tank