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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:

Pliers, screwdriver

Applicable Models:

Mercedes-Benz C350 (2007-14)
Mercedes-Benz CLK350 (2006-09)
Mercedes-Benz E350 (2006-14)
Mercedes-Benz GLK350 (2010-12)
Mercedes-Benz ML350 (2006-14)
Mercedes-Benz R350 (2006-12)
Mercedes-Benz S350 (2006, 2012-13)
Mercedes-Benz SLK350 (2005-14)

Parts Required:

New expansion tank, coolant

Hot Tip:

Replace the tank with the engine COLD

Performance Gain:

A major cooling system leak fixed

Complementary Modification:

Flush cooling system

Over time, the coolant expansion tank tends to turn yellow with age, become brittle forming micro fractures and 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 the car starts 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. Warning: Failure to repair or replace a leaking cooling system component can potentially cause a catastrophic failure damaging the engine. In our tank it was obvious as the overflow hose nipple broke off.

A couple of safety precautions/instructions you will want to observe before beginning include: allow the cooling system to cool down to a coolant temperature of less than 90°C; open the cap of the 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. NEVER pour coolant into beverage bottles, cups, etc. Someone might accidentally pick that cup up and start to drink.

New coolant technology means that coolants can last a very long time now. If your coolant is good there is no need to drain the system to replace the expansion tank. If you 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.

The coolant expansion tank or reservoir is located at the front right side of the engine compartment (red arrow).
Figure 1

The coolant expansion tank or reservoir is located at the front right side of the engine compartment (red arrow). You will need to remove the right side air duct (yellow arrow) as well as the front engine cover (green arrow) to replace the tank.

To remove the front engine cover simply pull up on the front of the cover and remove it (red arrow).
Figure 2

To remove the front engine cover simply pull up on the front of the cover and remove it (red arrow).

Remove the air duct by compressing the back of the engine cover and then sliding it off the front air duct (red arrow).
Figure 3

Remove the air duct by compressing the back of the engine cover and then sliding it off the front air duct (red arrow).

Remove the overflow line from the top front of the tank by using a small flathead screwdriver and lifting up on the release clip (red arrow) and pulling the hose out from the tank.
Figure 4

Remove the overflow line from the top front of the tank by using a small flathead screwdriver and lifting up on the release clip (red arrow) and pulling the hose out from the tank. Sometimes it helps to push the hose in before pulling it out.

The tank has a supply line on the bottom of it (red arrow) that feeds the radiator (yellow arrow).
Figure 5

The tank has a supply line on the bottom of it (red arrow) that feeds the radiator (yellow arrow). If you are not draining and flushing the coolant system you can use a turkey baster or fluid pump to remove as much coolant as possible from the tank.

Disconnect the level sensor harness from the tank (red arrow).
Figure 6

Disconnect the level sensor harness from the tank (red arrow).

Pull up and remove the rubber trim from behind the tank.
Figure 7

Pull up and remove the rubber trim from behind the tank.

Use a small flathead screwdriver and gently pry up and remove the clip that holds the wiring harness to the firewall (red arrow).
Figure 8

Use a small flathead screwdriver and gently pry up and remove the clip that holds the wiring harness to the firewall (red arrow).

Pull back on the two tabs on the top of the tank mount (red arrows) and slide the two prongs on the mount (yellow arrows) up and out from the fire wall.
Figure 9

Pull back on the two tabs on the top of the tank mount (red arrows) and slide the two prongs on the mount (yellow arrows) up and out from the fire wall.

You can now pull the mount out from the grommet it sits in (red arrow).
Figure 10

You can now pull the mount out from the grommet it sits in (red arrow). If you have not drained the system you will want to clamp off the hose to the tank with hose clamps pliers or vice grips wrapped in a rag. Remove the hose clamp and install the new tank (yellow arrow). If you are quick and hold the hose upright you can remove the old tank and install the new one without much loss of coolant. Installation is the reverse of removal.

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Page last updated: Mon 12/5/2016 02:52:51 AM