Mercedes W123 Fuel Cap And Oil Cap Seal Replacement Repair Guide

Difficulty

Very easy

Steps

Time Required

                          5 minutes

Sections

Fuel Cap and Oil Cap Seal
3 steps

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Introduction

Some fluid leaks are very difficult to fix and so we live with them until time and money allows us to fix them; however, others are very easy to fix. Start by fixing the easy ones to at least lessen the amount of fluid your car leaves behind.

One often overlooked spot for fuel and oil leaks are the seals on the respective caps.

Both the fuel cap and oil cap have rubber seals that prevent the fluids inside from flowing out from underneath the cap. If you’re seeing any evidence of oil or fuel leaking out from underneath the respective caps it’s time to replace those rubber seals. Learn to do it yourself, and avoid buying an entire new cap!

Note - there are two styles of oil cap that you may find on your car. One is the older metal style that was originally equipped on these cars. The second is a newer style black plastic cap. Mercedes no longer makes replacement metal caps so if your car is equipped with a metal cap it’s even more important to learn to replace the seal so you can keep your original cap! The trick here is that no one sells a specific seal for the old style metal oil cap. However, the great news is that the seal that is sold for the metal fuel cap will fit just fine on the oil cap. So if you have a metal oil cap, simply order two of the fuel cap seals instead of ordering the plastic style oil cap seal.

What you need

Step 1

              Fuel Cap and Oil Cap Seal

As noted in the introduction there are two styles of oil caps. One of the cars used in the creation of this guide has the old style metal oil cap. Therefore, two fuel cap seals will be used; one for the fuel cap, and one for the oil cap. These are pictured.
The other car used has the new style plastic cap. In this case, you’ll need one fuel cap seal, and one plastic oil cap seal.

As noted in the introduction there are two styles of oil caps. One of the cars used in the creation of this guide has the old style metal oil cap. Therefore, two fuel cap seals will be used; one for the fuel cap, and one for the oil cap. These are pictured.

The other car used has the new style plastic cap. In this case, you’ll need one fuel cap seal, and one plastic oil cap seal.

1024

Step 2

Remove the first cap that is leaking. In this picture, it is the fuel cap.
Using a flat blade screwdriver, gently lift the old seal out. In the case of the old black fuel seal pictured, it was very brittle; it had become about as flexible as plastic instead of rubber.
Install the new seal, stretching it around the two metal tabs that extend out of the center of the cap.
Repeat with the next cap, in this case the metal oil cap. That seal was still fairly soft, and was not leaking on this car, but was replaced as preventative maintenance.

Remove the first cap that is leaking. In this picture, it is the fuel cap.

Using a flat blade screwdriver, gently lift the old seal out. In the case of the old black fuel seal pictured, it was very brittle; it had become about as flexible as plastic instead of rubber.

Install the new seal, stretching it around the two metal tabs that extend out of the center of the cap.

Repeat with the next cap, in this case the metal oil cap. That seal was still fairly soft, and was not leaking on this car, but was replaced as preventative maintenance.

Step 3

Alternatively, replace the seal on your new style plastic oil filler cap.
This seal is thinner, and a bit harder to remove. Gently pull it out with needle nose pliers being careful not to damage the cap.
Just like the seal on the fuel cap previously pictured, this seal is somewhat hardened and has a permanent groove in it. Replacing it with a new seal will likely stop the oil staining no the valve cover around it.

Alternatively, replace the seal on your new style plastic oil filler cap.

This seal is thinner, and a bit harder to remove. Gently pull it out with needle nose pliers being careful not to damage the cap.

Just like the seal on the fuel cap previously pictured, this seal is somewhat hardened and has a permanent groove in it. Replacing it with a new seal will likely stop the oil staining no the valve cover around it.

Once the seals are replaced simply re-install the caps. After driving, check for any leaks and try to re-seat the seals if there are any.

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                    Nicolas Siemsen

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basher464 - May 2, 2016

My car the flow of oil by oil cap where the problem I will thanks if you guide me how to do

carste10 - Nov 8, 2018

I replaced my fuel filler cap sal with the blue nitrile? seal and it does seal. But!!! when t was time to refuel (approx 2 wks) the cap was extremely hard to break loose. Much too hard for my wife to open. So I applied some silicone grease. That helped but only one cycle worth. Seems diesel fuel dissolves the grease. So I’m back to replacing the $18 blue gasket with a regular gasket.

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