How To Purge Your Mercedes W123 Diesel Repair Guide

Difficulty

Very easy

Steps

Time Required

                          20 minutes

Sections

How to purge your Mercedes W123 diesel
7 steps

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Introduction

The ideal time to do this is just before you plan to change both of your fuel filters as they should always be replaced after a purge.

What you need

Step 1

              How to purge your Mercedes W123 diesel

To begin, loosen the clamp on the rubber fuel hose that connects to the supply hard line. The supply line is the lower of the two, where the hose goes to the clear plastic pre-filter.

To begin, loosen the clamp on the rubber fuel hose that connects to the supply hard line. The supply line is the lower of the two, where the hose goes to the clear plastic pre-filter.

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Step 2

Pull the fuel hose off. Be aware that some fluid will run out of the supply line as you remove the hose. More will flow if you have a full tank of fuel.
Have a plug ready, made using a small length of fuel hose and a tightly fitting bolt.

Pull the fuel hose off. Be aware that some fluid will run out of the supply line as you remove the hose. More will flow if you have a full tank of fuel.

Have a plug ready, made using a small length of fuel hose and a tightly fitting bolt.

Step 3

Next, loosen the rearmost clamp on the fuel return “cigar” shaped hose that is larger in the middle than the ends. This is the connection to the hard fuel return line that takes unburnt fuel back to the tank.
Remove this line. Little fluid should run out.

Next, loosen the rearmost clamp on the fuel return “cigar” shaped hose that is larger in the middle than the ends. This is the connection to the hard fuel return line that takes unburnt fuel back to the tank.

Remove this line. Little fluid should run out.

Step 4

Attach a 12" or so length of 5/16" fuel line on the supply and return lines, using appropriately sized barbed fittings to create hose extensions to make it easier to insert the hoses in your temporary “fuel tank”.

Attach a 12" or so length of 5/16" fuel line on the supply and return lines, using appropriately sized barbed fittings to create hose extensions to make it easier to insert the hoses in your temporary “fuel tank”.

Step 5

You’ll need to create a small temporary “fuel tank” for the diesel purge. Any plastic bottle will work. You’ll want to cut a hole in it for the supply hose so that the hose can reach the very bottom of the “tank”.

You’ll need to create a small temporary “fuel tank” for the diesel purge. Any plastic bottle will work. You’ll want to cut a hole in it for the supply hose so that the hose can reach the very bottom of the “tank”.

Step 6

Fill your temporary “fuel tank” up with the diesel purge fluid.
Now insert the return line in the top of the tank. It can be above the level of the fluid. It will just be pouring fuel back in to the tank.

Fill your temporary “fuel tank” up with the diesel purge fluid.

Now insert the return line in the top of the tank. It can be above the level of the fluid. It will just be pouring fuel back in to the tank.

Step 7

Now, start the engine!
Let the car run. It will take in the purge, burn some of it, and return some of it to the tank. As it flows through the system it will clean the system. You may see that the purge comes out darker than it goes in.
As it flows through, any carbon removed from the system will get trapped in the filters.
Stop the car just before the purge goes below the level of the supply line. Do not let your tank run dry or you’ll have a hard time removing the air from your fuel system!
After running a purge, it’s the perfect time to replace your fuel filters. There are two guides to help with this.
Primary Fuel Filter Replacement
Secondary Fuel Filter Replacement

Now, start the engine!

Let the car run. It will take in the purge, burn some of it, and return some of it to the tank. As it flows through the system it will clean the system. You may see that the purge comes out darker than it goes in.

As it flows through, any carbon removed from the system will get trapped in the filters.

Stop the car just before the purge goes below the level of the supply line. Do not let your tank run dry or you’ll have a hard time removing the air from your fuel system!

After running a purge, it’s the perfect time to replace your fuel filters. There are two guides to help with this.

Primary Fuel Filter Replacement

Secondary Fuel Filter Replacement

When done, re-attach the fuel supply and return lines to the appropriate hard lines.

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                    Nicolas Siemsen

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What you need

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