Mercedes W123 Fuel Return Line Replacement Repair Guide

Difficulty

Very easy

Steps

Time Required

                          15 minutes

Sections

Fuel Return Line
6 steps

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Introduction

You’ll need to keep an even closer eye on them if you run biodiesel. If you use 99% biodiesel they may only last a year. Biodiesel literally dissolves rubber!

Learn to replace them now, and keep some spare in your trunk for emergencies.

What you need

Step 1

              Fuel Return Line

As shown here, the injector return lines go from one injector to the next.
And then they stop with a plug at the rearmost injector, closest to the firewall.

As shown here, the injector return lines go from one injector to the next.

And then they stop with a plug at the rearmost injector, closest to the firewall.

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Step 2

The lines should simply pull off of the injector nipples.
These lines were fairly stiff, but not brittle yet. However, it’s a good time to replace them. Once they become brittle the can become very hard to remove. They will break off at the nipple and they will need to be cut off with a razor blade, very carefully, to avoid scoring the metal nipples.

The lines should simply pull off of the injector nipples.

These lines were fairly stiff, but not brittle yet. However, it’s a good time to replace them. Once they become brittle the can become very hard to remove. They will break off at the nipple and they will need to be cut off with a razor blade, very carefully, to avoid scoring the metal nipples.

Step 3

Notice how much larger the opening at the end of the old injector return line, left, is than the one on the right, which is new.
As the lines become brittle they seal less well at the nipples due to this.
Now, cut a length of new line to approximately the same length as the old line. You can err on the side of being a bit too long to make it easier to install.

Notice how much larger the opening at the end of the old injector return line, left, is than the one on the right, which is new.

As the lines become brittle they seal less well at the nipples due to this.

Now, cut a length of new line to approximately the same length as the old line. You can err on the side of being a bit too long to make it easier to install.

Step 4

Installation is simply the reverse; push the new line down on to the nipples on the injector.
It can help to do just one at a time, so you don’t mix up which line goes where.
Another helpful tip is to use a small needle nose plier to start the line on the injector nipple when the space if too tight for your fingers.

Installation is simply the reverse; push the new line down on to the nipples on the injector.

It can help to do just one at a time, so you don’t mix up which line goes where.

Another helpful tip is to use a small needle nose plier to start the line on the injector nipple when the space if too tight for your fingers.

Step 5

Don’t forget to replace the long piece of line that runs from the front-most injector to the secondary fuel filter housing.
It starts here at the front-most injector.
And connects here at the filter housing.

Don’t forget to replace the long piece of line that runs from the front-most injector to the secondary fuel filter housing.

It starts here at the front-most injector.

And connects here at the filter housing.

Step 6

Also, be sure to change the plug on the rear-most injector nipple.
The one removed from this car was a braided line with a metal plug in it.
The one being installed is a special rubber plug that only has one opening.
You can also make one yourself, using a short piece of regular return line and a tightly fitting screw that can be securely inserted in one end of the short line.

Also, be sure to change the plug on the rear-most injector nipple.

The one removed from this car was a braided line with a metal plug in it.

The one being installed is a special rubber plug that only has one opening.

You can also make one yourself, using a short piece of regular return line and a tightly fitting screw that can be securely inserted in one end of the short line.

Once you’re done priming, start the engine and let it run momentarily to ensure it’s primed properly.

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                    Nicolas Siemsen

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Simon Walter-Hansen - Nov 21, 2018

What size diameter and fuel line material should I get as a replacement?

Will MacNeill - Jan 7, 2019

The lines are available in Viton as well, which is biodiesel compatible:

617/616: https://www.amazon.com/dp/B07L6SS6B6

603/602/601: https://www.amazon.com/dp/B07L6QTYS1

Catherine - Oct 21, 2019

I redid my lines after paying a shop here in Granbury,TX 1400.00 to replace my fuel injection system..thier tech told me when I picked my 83 Benz 300D Turbo up..that he had no idea what he was doing..after the fact..he put plain rubber hoses on her that melted on the way home.. I’m a 60 yr old female whose worked on cars for 50yrs, never have I seen such poor service..as this shop.

Introduction#

What you need#

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Introduction

What you need

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