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Coolant Flush and Replacement
 
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Pelican Technical Article:

Coolant Flush and Replacement

Steve Vernon

Time:

2 hours2 hrs

Tab:

$20 to $50

Talent:

**

Tools:

Flathead screwdriver, large bucket

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

Coolant

Hot Tip:

Get a really big bucket

Performance Gain:

Fresh coolant

Complementary Modification:

New hoses

Modern coolants last a very long time and if you need to drain your coolant to work on other parts of the vehicle you really should consider draining it into a clean container so you can reuse it. This article will show you how to drain the coolant system, flush the radiator and fill and bleed the system. This is also a very good time to check the condition of your hoses.

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, into the ground or a sewer.

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.

Working on the top of the motor first you will see the radiator (red arrow), the expansion reservoir (yellow arrow) and the top hose that connects the top of the radiator to the thermostat housing (blue arrow).
Figure 1

Working on the top of the motor first you will see the radiator (red arrow), the expansion reservoir (yellow arrow) and the top hose that connects the top of the radiator to the thermostat housing (blue arrow).

Begin by opening the cap on the expansion reservoir to break the vacuum in the system.
Figure 2

Begin by opening the cap on the expansion reservoir to break the vacuum in the system. Make sure the coolant is cool before releasing the pressure. If the coolant is still hot and under pressure you can seriously hurt yourself.

There are two mounts for the radiator under the front of the car, one is just a mount (yellow arrow) and the other is the mount and drain plug (red arrow).
Figure 3

There are two mounts for the radiator under the front of the car, one is just a mount (yellow arrow) and the other is the mount and drain plug (red arrow).

Place a large bucket under the drain plug and use a flathead screwdriver to open the plug.
Figure 4

Place a large bucket under the drain plug and use a flathead screwdriver to open the plug. If you are going to reuse the coolant make sure to drain it into a clean container.


NOTE: There is also an engine block drain on passenger side of the engine above the motor mount. To fully drain the old coolant this must be done as well, the block holds a substantial amount. It will go everywhere when released and is not fun.

The drain plug will unscrew and then pull out from the bottom.
Figure 5

The drain plug will unscrew and then pull out from the bottom. Make sure to check the condition of the plug for damage as this can lead to potential leaking.

Use a flathead screwdriver and remove the clamp from the upper hose and carefully pull it back off the radiator.
Figure 6

Use a flathead screwdriver and remove the clamp from the upper hose and carefully pull it back off the radiator. The top of the radiator is plastic and is known for breaking off. If your hose is stuck, do not just pull on it, try running a small flathead screwdriver or pick around the hose to break the seal.

Next use a flathead screwdriver and remove the clamp and hose from the top hose to thermostat housing (red arrow).
Figure 7

Next use a flathead screwdriver and remove the clamp and hose from the top hose to thermostat housing (red arrow). Be prepared for coolant to escape when you remove this hose.

There are two hoses that connect to the bottom of the radiator; the thermostat hose (red arrow) and the supply hose from the expansion reservoir (yellow arrow).
Figure 8

There are two hoses that connect to the bottom of the radiator; the thermostat hose (red arrow) and the supply hose from the expansion reservoir (yellow arrow). Remove these hoses and allow the remaining coolant to drain out. If you would like to flush out the radiator and block insert a garden hose into the top of the radiator and turn it on until the water runs clear out of the bottom. Make sure to catch this water and dispose of it properly. Next insert the hose into the top of the thermostat housing and preform he same procedure. Check your hoses and reattach everything. You will fill the system by filling the expansion reservoir. Once the system is full you will want to get the air out, to do this start the car with the reservoir cap off and let the motor run. As air escapes through the expansion reservoir you need to be prepared to add coolant. Once the air is out, top up the reservoir until you have the correct level. Check for leaks and you are done.

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Comments and Suggestions:
KeegsF1 Comments: There is also an engine block drain on passenger side of the engine above the motor mount. To fully drain the old coolant this must be done as well, the block holds a substantial amount. It will go everywhere when released and is not fun. This should be covered/added to the article. Cheers
October 4, 2016
  Followup from the Pelican Staff: Thanks for the additional info. We appreciate it. I will have the article updated.
- Nick at Pelican Parts
 

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