Hi, just looking for advice on changing the fuel lines in the picture. Is it as simple as removing and replacing or will the system need bleeding. Also I measured the plastic pipe as 5.7 with not very accurate caliper. Anyone know the size I'm guessing 5.6. Thanks for any help.

Mark.

If that is the return line, not the delivery line, then it will not need to be bled.

The outside diameter is unimportant; it's the internal diameter that needs to match your existing hose to ensure a snug fit on the metal pipe.

Ensure the hose is suited to the fuel. Not all grades of hose can be used on both diesel and petrol.

Thank you for the advice it is the pipe with a blue marking on. I'm not sure how to identify return and delivery. The pipe it attaches to is actually plastic. A friend said to cut it further up to avoid the tight turn.?

I am not familiar with the A4 so I can not be more specific.

A large radius bend will put less strain on the hose than a small radius, but don't go to extremes. You don't want such a large radius that it flops around or rubs against other components.

If the outer diameter of the plastic pipe is 5.6/5.7 mm I would buy fuel pipe with internal bore of 5mm and warm in boiling water for a few minutes before fitting, secure with clamps of correct diameter for hose outer diameter, be quick when replacing and when starting give it a boot of revs for a few minutes and with any luck the air will be pushed thru with  the revs fluttering a few times. 

Thank you I had bought 5.6mm pipe but will change to 5mm. Thank you for the advice rev the engine to hopefully avoid having to bleed the system.

If you’ve managed to get the exact pipe for the diameter then that’s great. Just make sure it’s secure and not leaking or sucking air, once all connected you can smear abit grease on the joint and use that as a indicator for leaks or suction 

Thanks will do. What do you think about cutting the plastic pipe a bit shorter to reduce the tight angle?

Edited January 15, 20251 yr by Arnie11

Thats up to you, but you would need to cut back to a straight section because sealing the new hose on a bend will be difficult.