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Coolant Flush and Replacement
 
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Pelican Technical Article:

Coolant Flush and Replacement

Steve Vernon

Time:

4 hours4 hrs

Tab:

$4 to $100

Talent:

**

Tools:

Flathead screwdriver, 8mm socket, large bucket

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

Hoses, coolant

Hot Tip:

If there is any question, replace the hose

Performance Gain:

No leaks

Complementary Modification:

Coolant flush

There are not a lot of radiator hoses on the Mercedes-Benz W123 and most of them can be replaced without removing other components. I recommend inspecting your rubber hoses every two years or so. As they age, they have a tendency to get hard and brittle. When you gently squeeze a hose, it should be relatively soft and easy to indent with your hand. It shouldn't feel like it is brittle or crunching when you squeeze it. It should spring back to its original shape pretty quickly after being compressed. If it feels very hard, then it might be time to replace it. If there is a bulge in the hose, or any type of crack in the surface of the hose, then you should replace it as well. Also check for leaks around where the hoses create their connections--that is a sign that the hose should be replaced.

A couple of safety precautions/instructions you may want to observe before beginning:

Allow cooling system to cool down to a coolant temperature of less than 90°C. Open the cap of cooling system slowly; turn a conventional coolant cap as far as the first detent and turn a screwed coolant cap approx. 1/2 turn and release the pressure. Wear protective gloves, protective clothing and eye protection. Always dispose of used coolant in accordance with the regulations in your region; NEVER pour coolant down a drain, on the ground or into a sewer.

This article will identify the hose and show the procedures for replacement. Begin by safely jacking up and supporting your car. Please see our article on these procedures for additional help.

Remember your car may have been serviced before and parts replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If working with the electrical system, disconnect the battery before beginning. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.

Our vehicle may vary slightly from yours as models do change and evolve as they grow older. If something seems different, let us know and share your info to help other users. Questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

With the exception of the expansion tank to radiator overflow hose you are going to need to drain the coolant to replace the hoses.
Figure 1

With the exception of the expansion tank to radiator overflow hose you are going to need to drain the coolant to replace the hoses. Please see our article on coolant flush and drain for additional assistance. If your coolant is old, this is a good time to replace it and flush your radiator, if it is new there is no reason you cannot reinstall it into the vehicle as long as you drain it into a clean container.

There are two hoses visible from the top of the engine: the radiator to expansion tank overflow hose (red arrow) and the radiator to thermostat housing hose (yellow arrow).
Figure 2

There are two hoses visible from the top of the engine: the radiator to expansion tank overflow hose (red arrow) and the radiator to thermostat housing hose (yellow arrow).

To replace the top hose use a flathead screwdriver and remove the clamps where the hose joins the radiator (yellow arrow) and the thermostat housing (red arrow).
Figure 3

To replace the top hose use a flathead screwdriver and remove the clamps where the hose joins the radiator (yellow arrow) and the thermostat housing (red arrow).

The top of the radiator is made out of plastic and is known to break.
Figure 4

The top of the radiator is made out of plastic and is known to break. When removing the hose run a thin flathead screwdriver between the hose and radiator opening to help break the seal. Do not just try and force it off or you run the risk of breaking the radiator and having to replace it.

There is a small hose that handles the overflow from the radiator and runs it to the expansion tank (red arrow).
Figure 5

There is a small hose that handles the overflow from the radiator and runs it to the expansion tank (red arrow).

Use a flathead screwdriver to loosen the clamp and remove the hose from both the radiator and expansion tank.
Figure 6

Use a flathead screwdriver to loosen the clamp and remove the hose from both the radiator and expansion tank. Remember to use care when removing it from the plastic nipple on the radiator.

At the bottom of the expansion tank is the supply hose to the radiator.
Figure 7

At the bottom of the expansion tank is the supply hose to the radiator. It is a tight fit but use a short flathead screwdriver to remove the clamp and hose from the tank (red arrow).

On the same right side of the motor is the hose from the lower thermostat housing to the bottom right of the radiator.
Figure 8

On the same right side of the motor is the hose from the lower thermostat housing to the bottom right of the radiator. Use a short flathead screwdriver and loosen the hose clamp and remove the hose from the lower thermostat housing (red arrow).

If you are replacing the expansion tank supply hose (red arrow) and it still has its original hardware and clamp, you will need to remove the air filter housing to access the supply hose mount (blue arrow).
Figure 9

If you are replacing the expansion tank supply hose (red arrow) and it still has its original hardware and clamp, you will need to remove the air filter housing to access the supply hose mount (blue arrow). Use an 8mm socket and remove the bracket. In this image you can also see the lower thermostat housing to radiator hose (yellow arrow).

There is a short hose that goes between the thermostat housing and coolant pump (red arrow).
Figure 10

There is a short hose that goes between the thermostat housing and coolant pump (red arrow). Depending on which way the clamps are facing, you will either need to remove the air filter housing or the drive belts. This hose is easier to replace when replacing the thermostat housing or the water pump.

Working from under the vehicle you can remove the clamps for the lower thermostat to radiator hose (red arrow) and the expansion tank supply hose (yellow arrow).
Figure 11

Working from under the vehicle you can remove the clamps for the lower thermostat to radiator hose (red arrow) and the expansion tank supply hose (yellow arrow). Installation is the reverse of removal. You do not need to over tighten the hose clamps, especially on the plastic radiator connections, just firm them up and if they are leaking a little give them a little more tightening. Do not forget to refill and bleed the coolant.

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