How much fuel passes through the "return" line ?

[Ireland]

I've been trying to pinpoint the exact spot where I have a fuel leak in my engine bay and the feed pipe from the pump to the fuel rail seems fine but there is a crack in the return line where it had rubbed off the engine block.

How much fuel is actually "returned" via this?

Would it be flowing through it continuously or is it only occassionally that fuel would be in it?

I'm going to replace the pipes regardless but I'd like to be sure I'd solved the problem as well as just fitting new lines.

[Tanguero]

It is a continuous flow. At least it should be unless your engine is using more fuel than the pump can supply.

I found a good tip for detecting hard to spot fuel leaks that evaporate as soon as they appear is to dust the suspect area with talc. You can often see the talc being disturbed where you can't see the leak its self.

[Walford]

Ireland said:

How much fuel is actually "returned" via this?

Would it be flowing through it continuously or is it only occassionally that fuel would be in it?

Depends on how wide injector pulse is (load/rpm) but at max you must maintain constant pressure in fuel rail, so on idle quiet a lot will be returned

[Ireland]

I'd say I have it found so.



One thing I've noticed is that the supply pipe has an ID of 8mm and the return pipe has an ID of 7mm

Is this normal or should they both be 8mm pipes?

The fittings that the return line attaches to are all 8mm OD and the hose does seem to be stretched to fit over them.

Edited by Ireland on Monday 12th August 15:35

[Tanguero]

All the original fuel hoses on mine ('98 4.2) were 7mm id.