Difficulty

Very easy

Steps

7

Time Required

                          5 minutes

Sections

1

  • Checking coolant level in your naturally aspirated diesel Mercedes W123
  • 7 steps

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Introduction

What you need

Step 1

              Checking coolant level in your naturally aspirated diesel Mercedes W123
  • Before proceeding very carefully check that the coolant temperature is low enough to safely check the coolant level.
  • To do this use your hand to carefully check and see how hot the radiator cap is. It should be cool to the touch. If it is hot, or even warm, it is best to wait. If you have recently driven the car it can take several hours before the coolant has cooled enough to check the level.
  • Never remove a hot to the touch cap on a radiator. It can lead to rapid and violent discharge of scalding hot coolant which can cause very serious injury.

Before proceeding very carefully check that the coolant temperature is low enough to safely check the coolant level.

To do this use your hand to carefully check and see how hot the radiator cap is. It should be cool to the touch. If it is hot, or even warm, it is best to wait. If you have recently driven the car it can take several hours before the coolant has cooled enough to check the level.

Never remove a hot to the touch cap on a radiator. It can lead to rapid and violent discharge of scalding hot coolant which can cause very serious injury.

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Step 2

  • Once you have verified that the coolant is cool enough to proceed, use the palm of your hand to press down on the radiator cap and turn it counter clockwise.

Once you have verified that the coolant is cool enough to proceed, use the palm of your hand to press down on the radiator cap and turn it counter clockwise.

Step 3

  • The cap will turn about 90 degrees counterclockwise; this is the first stop and allows any residual pressure to be released without the cap coming off.
  • Continue to turn the cap another approximately 45 degrees until it stops turning.

The cap will turn about 90 degrees counterclockwise; this is the first stop and allows any residual pressure to be released without the cap coming off.

Continue to turn the cap another approximately 45 degrees until it stops turning.

Step 4

  • Pull the cap up and out of the radiator and set it aside.

Pull the cap up and out of the radiator and set it aside.

Step 5

  • Look down in to the neck of the radiator. The coolant should reach up or very near to the bottom rim of the neck.
  • If the coolant reaches this point the level is fine and the cap can be replaced.

Look down in to the neck of the radiator. The coolant should reach up or very near to the bottom rim of the neck.

If the coolant reaches this point the level is fine and the cap can be replaced.

Step 6

  • If the coolant is low it should be topped off with half distilled water and half coolant, if using full-strength concentrated coolant.
  • Use only coolant that is certified for use in Mercedes-Benz engines. These are usually nearly clear, if perhaps a light orange or yellow in color. They are phosphate-free and are designed not to react with certain metals in the engine. You can use Genuine Mercedes-Benz coolant, or an alternative such as the one pictured.
  • Be aware that if you use regular green coolant it may lead to engine damage in the long term.
  • Never mix coolants. If you find your cooling system is filled with green coolant top it off with the same type of coolant but plan to change the coolant out and flush the system in the near future.

If the coolant is low it should be topped off with half distilled water and half coolant, if using full-strength concentrated coolant.

Use only coolant that is certified for use in Mercedes-Benz engines. These are usually nearly clear, if perhaps a light orange or yellow in color. They are phosphate-free and are designed not to react with certain metals in the engine. You can use Genuine Mercedes-Benz coolant, or an alternative such as the one pictured.

Be aware that if you use regular green coolant it may lead to engine damage in the long term.

Never mix coolants. If you find your cooling system is filled with green coolant top it off with the same type of coolant but plan to change the coolant out and flush the system in the near future.

Step 7

  • Make sure the cap is fully tightened. After your next drive check the cap for leaks and tighten further if necessary.

Make sure the cap is fully tightened. After your next drive check the cap for leaks and tighten further if necessary.

To reassemble your device, follow these instructions in reverse order.

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                    Nicolas Siemsen

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zeny30 - Apr 2, 2017

Reply

Awesome guide, thank you so much! Getting my first W123 tomorrow, this will be very useful!

Rajat Singh - May 25, 2018

Reply

I have a 1984 W123 300D, which doesn’t have a coolant recovery bottle. I would like to have one fitted. Where is it suppose to be? I mean how close or far from the radiator? And at what level/height as compared to the radiator? I believe the level/height of the radiator cap and the bottle cap has to be the same.