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Coolant Expansion Tank Replacement
 
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Pelican Technical Article:

Coolant Expansion Tank Replacement

Tom Morr

Time:

1 hour1 hr

Tab:

$70

Talent:

**

Tools:

8mm, 10mm socket, pliers, screwdrivers

Applicable Models:

Mercedes-Benz SLK230 (1998-04)

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, become brittle and form 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.

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

Allow cooling system to cool down. 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. NEVER pour coolant into beverage bottles, cups, etc. Someone might accidentally pick that cup up and start to drink.

If the coolant in the car is new there is no reason to replace it as long as you drain it into a clean container. Coolant is expensive and not great for the environment so if the coolant in your car is good, try and save it to reuse.

Begin by safely jacking up and supporting your car. With the car safely off the ground you will need to remove the engine tray. There are four 8mm bolts holding the tray on.

With the tray removed you will see radiator drain plug on the lower left front of the car. Place a catch bucket or tray under the plug and use a large flat head screwdriver to open the drain plug. The fluid drains out a small spigot facing rearward and not through the red plug. If you attach a clean drain hose to the spigot it will make safely capturing the coolant easier. You do not need to drain all the coolant from the car, but just enough to get below the lower hose connection on the tank. If you are going to flush or replace the coolant, drain completely.

Working from the top you will need to; remove the cap (which if good you can reuse), the two 10mm bolts holding the tank to the cross member, the overflow tube and the hose running from the tank to the thermostat.

Working from the side you will need to loosen the hose clamp and remove the hose to the radiator.

Slip the tank from the mounting grommet and remove.

If you where not having problems with the level sensor remove the old one by turning it 45 degrees and install it in the new tank.

Installation is the reverse of removal

Begin by safely jacking up and supporting your car.
Figure 1

Begin by safely jacking up and supporting your car. With the car safely off the ground you will need to remove the engine tray. There are four 8mm bolts holding the tray on (red arrows).

With the tray removed you will see radiator drain plug (yellow arrow) on the lower left front of the car.
Figure 2

With the tray removed you will see radiator drain plug (yellow arrow) on the lower left front of the car. Place a catch bucket or tray under the plug and use a large flat head screwdriver to open the drain plug. The fluid drains out a small spigot facing rearward (red arrow) and not through the red plug (yellow arrow).

If you attach a clean drain hose to the spigot it will make safely capturing the coolant easier.
Figure 3

If you attach a clean drain hose to the spigot it will make safely capturing the coolant easier. You do not need to drain all the coolant from the car, but just enough to get below the lower hose connection on the tank. If you are going to flush or replace the coolant, drain completely.

Working from the top you will need to; remove the cap (green arrow, which if good you can reuse), the two 10mm bolts holding the tank to the cross member (yellow arrows), the overflow tube (green arrow) and the hose running from the tank to the thermostat (red arrow).
Figure 4

Working from the top you will need to; remove the cap (green arrow, which if good you can reuse), the two 10mm bolts holding the tank to the cross member (yellow arrows), the overflow tube (green arrow) and the hose running from the tank to the thermostat (red arrow).

Working from the side you will need to loosen the hose clamp and remove the hose to the radiator (red arrow).
Figure 5

Working from the side you will need to loosen the hose clamp and remove the hose to the radiator (red arrow). Note: the shroud has been removed to better illustrate the hose.

This photo illustrates the tank out of the car.
Figure 6

This photo illustrates the tank out of the car. You can see: the mounting post that sits in the rubber grommet (blue arrow), the level sensor housing (red arrow), the thermostat line (yellow arrow) and the main hose line (green arrow).

If you where not having problems with the level sensor remove the old one by turning it 45 degrees and install it in the new tank (red arrow).
Figure 7

If you where not having problems with the level sensor remove the old one by turning it 45 degrees and install it in the new tank (red arrow).

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Comments and Suggestions:
Rob Comments: Hi the hose going from the thermostat to the coolant expansion tank has deteriorated under the clip. It's the one with the metal element at the end that joins the coolant tank. Can I get a replacement from anywhere or will it have to be a repair Job? I couldn't see one on your website. Thanks!
April 30, 2017
  Followup from the Pelican Staff: You will need the right molded hose to fix it. I’m not the best with part numbers, I am the technical question person.

Give The Pelican Parts parts specialists a call at 1-888-280-7799. They can figure out what part or repair kit you need.
- Nick at Pelican Parts
 
Ken Comments: will there be any problem if I only work from the top, i.e. not drain out the coolant from bottom but just pump out coolant from from the tank through the radiator cap opening using fishing tank pump?
June 16, 2016
  Followup from the Pelican Staff: You may have some spill, so be prepared to catch it. - Nick at Pelican Parts  
zullharon Comments: is there a pressure switch in slk280 raditor. safety pressure valve
May 10, 2015
  Followup from the Pelican Staff: For over-pressure situations? The expansion tank cap allows excess pressure to bleed. Not aware of another valve that does this. - Nick at Pelican Parts  

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Page last updated: Tue 10/17/2017 02:32:35 AM