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Coolant Expansion Tank Replacement
 
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Pelican Technical Article:

Coolant Expansion Tank Replacement

Steve Vernon

Time:

1 hour1 hr

Tab:

$35 to $70

Talent:

**

Tools:

8mm socket, flathead screwdriver

Applicable Models:

Mercedes-Benz W123 (1977-85)

Parts Required:

Expansion tank, coolant

Hot Tip:

Replace the tank with the engine COLD

Performance Gain:

Proper cooling of the engine

Complementary Modification:

Flush cooling system

Over time, the coolant expansion tank tends to turn yellow with age, becomes brittle and forms micro fractures that can sometimes leak. When the car warms up, both the heat and pressure of the coolant starts to attack the weakest point of the tank, eventually causing it to fail and start leaking coolant. The good news is that the replacement tank is relatively inexpensive and can be changed in less than an hour.

Take a look around the coolant tank. In some instances, you can instantly see it has been leaking. In others, you may only see a faint trace of coolant weeping/staining the crack or seam. It's important to tackle this problem as soon as possible as failure to repair or replace a leaking cooling system component can potentially cause a catastrophic failure damaging the engine.

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 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. If you are replacing the coolant while replacing the reservoir make sure to dispose of it in accordance with the regulations in your area; never pour coolant down a drain, into the ground or into a sewer.

New coolant technology means that coolants can now last a very long time. If your coolant is good there is no need to throw it out, you can reuse it. If your coolant is failing, now would be a really good time to drain and flush the system. Please see our other articles on these procedures for additional assistance.

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.

The coolant expansion tank is located on the right side of the engine bay (red arrow).
Figure 1

The coolant expansion tank is located on the right side of the engine bay (red arrow). It is connected to the radiator by an overflow hose on the top (yellow arrow) and a supply hose on the bottom (not shown).

Open the cap to release pressure in the system, making sure the system is cool to the touch before opening.
Figure 2

Open the cap to release pressure in the system, making sure the system is cool to the touch before opening. If you open the reservoir cap while the system is hot or under pressure you can seriously hurt yourself.

You will need to drain the coolant system to below the bottom of the reservoir.
Figure 3

You will need to drain the coolant system to below the bottom of the reservoir. Please see our article on coolant flush and replacement for additional instruction.

Use a flathead screwdriver and remove the overflow hose (red arrow).
Figure 4

Use a flathead screwdriver and remove the overflow hose (red arrow). Gently pull the plastic expansion overflow hose of the neck of the reservoir (yellow arrow). This hose drains coolant to the ground in the case of a major overheating problem.

Use an 8mm socket and remove the three 8mm screws holding the reservoir in place (red arrows).
Figure 5

Use an 8mm socket and remove the three 8mm screws holding the reservoir in place (red arrows).

The lower supply hose is in a tight spot, use a short flathead screwdriver and remove the clamp and slide the hose off the reservoir (red arrow).
Figure 6

The lower supply hose is in a tight spot, use a short flathead screwdriver and remove the clamp and slide the hose off the reservoir (red arrow).

With the hose removed you can remove the reservoir from the vehicle.
Figure 7

With the hose removed you can remove the reservoir from the vehicle. Make sure to check the condition of the hoses. Installation is the reverse of removal. And do not forget to top up and bleed the cooling system.

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