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Pelican Technical Article:

Coolant Expansion Tank Removal

Kerry Jonsson

Time:

1 hour1 hr

Tab:

$100

Talent:

**

Tools:

10mm deep socket with ratchet and extension, flat head screwdriver, pliers

Applicable Models:

Mercedes-Benz R129 (1990-02)

Parts Required:

Coolant, coolant expansion tank, various hoses and clamps

Hot Tip:

Use clamping pliers to block hoses to prevent excessive loss of coolant

Performance Gain:

Replace cracked leaking expansion tank causing overheating.

Complementary Modification:

Replace hoses, clamps and radiator cap while doing the repair

Most European vehicles use a pressurized coolant expansion tank as a reserve for the cooling system. This has a few benefits. You can put a sensor in the tank to indicate to the driver when the coolant is low but the radiator and cooling systems are still full. The purpose of the expansion tank is simple. When coolant gets hot it expands and excessive coolant will spill out of the over flow hose. When the coolant cools it condenses and the coolant level drops. This may allow air into the system. You can have an overflow tank that is not pressurized like the cooling system but it will not bleed off air in the system. Air typically gets trapped at the highest point of the system. If you put the tank at the highest point in the system you can use it to bleed off air in the system without the use of bleeder screws and special procedures. In this tech article we will go over all the steps to remove the cooling expansion tank.

We strongly recommend you open and work on your cooling system when the car is cold. Cooling systems are under pressure to increase the boiling point of the coolant and if opened when hot steam and coolant will escape and can cause severe burns. Only ever open a cooling system when it is cold.

In order to replace your cooling system expansion tank you will need to remove the right side engine compartment cover. See our tech article on removing the engine covers. You do not have to remove all the engine covers, you only have to remove the right side engine cover.

Remove the right side engine cover.
Figure 1

Remove the right side engine cover. You can do this by removing the Phillips head screw (green arrow) that mounts it to another cover. See our tech article on removing engine covers.

Remove the radiator cap on a cold engine.
Figure 2

Remove the radiator cap on a cold engine. Here the radiator cap is already removed. If you have a siphon pump you can start by pumping the coolant out of the expansion tank. This makes the job a lot cleaner as opposed to draining the tank.

Remove the hose clamp of the hose coming out of the cap area on the expansion tank.
Figure 3

Remove the hose clamp of the hose coming out of the cap area on the expansion tank. Pull the hose off of the port. It may be held on by corrosion so twist is a few times before you pull it off.

Remove the lower hose clamp on the bottom of the expansion tank and pull the hose off.
Figure 4

Remove the lower hose clamp on the bottom of the expansion tank and pull the hose off. You can wait to dismount the tank before getting this clamp off but you will have to hold the tank with one hand and remove the clamp with the other. If the clamp is corroded this may be awkward.

Remove the larger hose clamp on the bottom of the expansion tank and pull off the hose.
Figure 5

Remove the larger hose clamp on the bottom of the expansion tank and pull off the hose.

Remove the smaller radiator air bleed hose clamp from the expansion tank and pull off the hose.
Figure 6

Remove the smaller radiator air bleed hose clamp from the expansion tank and pull off the hose.

At the bottom of the expansion tank squeeze each side of the electrical connector for the coolant level switch and pull the connector off.
Figure 7

At the bottom of the expansion tank squeeze each side of the electrical connector for the coolant level switch and pull the connector off.

Remove the two 10mm mounting fasteners (green arrows) that hold down the back of the expansion tank to the inner fender of the car.
Figure 8

Remove the two 10mm mounting fasteners (green arrows) that hold down the back of the expansion tank to the inner fender of the car. You can now pull the expansion tank out of the engine compartment.

Pull up firmly on the front of the expansion tank until the plastic lug unseats from the rubber grommet (green arrow) in the fender.
Figure 9

Pull up firmly on the front of the expansion tank until the plastic lug unseats from the rubber grommet (green arrow) in the fender. Installation is the reverse of the removal procedure. Fit the expansion tank plastic lug in the grommet in the fender and tighten the mounting fasteners. Fit the four hoses to their ports and tighten the clamps. Do not over tighten. You may damage the hoses and damage the expansion tank. Fill the coolant expansion tank with coolant up to the correct level. Start the engine and verify you do not have any leaks.

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Comments and Suggestions:
hank Comments: there is a hose on the bottom of the coolant expansion tank that runs to the radiator. where this hose connects to a 90 degree elbow broke off in the radiator. this elbow is replaceable.I dug out the remains of the old fitting and found a O ring that this elbow fits into the radiator. Do you have this fitting or do you know where I can find one? Thanks,Hank
January 29, 2016
  Followup from the Pelican Staff: It may be available separately. Give our parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 

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