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Mercedes Coolant Expansion Tank Replacement
 
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Pelican Technical Article:

Mercedes Coolant Expansion Tank Replacement

Steve Vernon

Time:

1 hour1 hr

Tab:

$60

Talent:

**

Tools:

10mm socket, pliers, screwdrivers

Applicable Models:

Mercedes-Benz C320 (2001-04)
Mercedes-Benz CLK320 (1998-04)
Mercedes-Benz E320 (1998-04)
Mercedes-Benz ML320 (1998-03)
Mercedes-Benz S320 (1998-99)
Mercedes-Benz SLK320 (2001-03)

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 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.

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

If you are going to be replacing the tank you might as well replace the coolant as well, as there may be the chance contaminants got into the tank and fluid. If it is an emergency and you need to get the car right back on the road it is possible to remove the coolant from the tank with a turkey baster and just replace the tank and lost coolant, but I recommend doing it right and draining the coolant. Even with the coolant drained you should expect a little spillage when removing the hoses, so be prepared for it.

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 six 8mm bolts holding the tray on, the rear two also help hold the transmission tray. If you are going to leave the transmission tray on, remove the rear two bolts first, lower the engine tray, reattach the transmission tray bolts, then remove the remaining four bolts on the engine tray.

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 screw driver to open the drain plug. The fluid will come out slowly at first so open the tank cap to break the vacuum and help speed things up. The fluid drains out a small spigot facing rearward and not through the red plug.

From the top of the tank you will need to remove the 10mm nut on the upper right side. The tank sits in a plastic slot in the firewall that helps support it.

Remove the right side air intake to give you more room to work on the hoses. It compresses in towards the engine then slips off.

With the air intake removed you can now pull the auxiliary water pump from its mount on the tank (it just pulls straight out) , remove the coolant level sensor plug along with the wires for the pump and sensor from the bracket on the front of the tank. Next, you want to remove the hose connected to the bottom of the tank. If the hose is original it will have a compression clamp on it, simply squeeze it together and you may have to use a small screw driver to help break the seal between the hose and tank. Be prepared to catch the small amount of coolant that will spill out.

Pull the tank straight up, it may take a little force as there is a small rubber grommet it sits in on the bottom.

Take the old tank to your bench and 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

With the car safely off the ground you will need to remove the engine tray.
Figure 1

With the car safely off the ground you will need to remove the engine tray. There are six 8mm bolts (red arrows) holding the tray on, the rear two also help hold the transmission tray. If you are going to leave the trans mission tray on, remove the rear two bolts first, lower the engine tray, reattach the transmission tray bolts, then remove the remaining four bolts on the engine tray.

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

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 screw driver to open the drain plug (yellow arrow).

The fluid will come out slowly at first so open the tank cap to break the vacuum and help speed things up.
Figure 3

The fluid will come out slowly at first so open the tank cap to break the vacuum and help speed things up. The fluid drains out a small spigot (yellow arrow) facing rearward and not through the red plug.

From the top of the tank you will need to remove the 10mm nut (red arrow) on the upper right side.
Figure 4

From the top of the tank you will need to remove the 10mm nut (red arrow) on the upper right side. The tank sits in a plastic slot (yellow arrow) in the firewall that helps support it. You can see where the overflow nipple broke off on our tank (green arrows).

Remove the right side air intake to give you more room to work on the hoses.
Figure 5

Remove the right side air intake to give you more room to work on the hoses. Compress it in towards the engine (red arrow) and remove it from the front air inlet.

With the air intake removed you can now pull the auxiliary water pump (green arrow) from its mount on the tank (it just pulls straight out), remove the coolant level sensor plug (yellow arrow) along with the wires for the pump and sensor from the bracket (blue arrow) on the front of the tank.
Figure 6

With the air intake removed you can now pull the auxiliary water pump (green arrow) from its mount on the tank (it just pulls straight out), remove the coolant level sensor plug (yellow arrow) along with the wires for the pump and sensor from the bracket (blue arrow) on the front of the tank. Next, you want to remove the hose connected to the bottom of the tank (red arrow). If the hose is original it will have a compression clamp on it, simply squeeze it together and you may have to use a small screw driver to help break the seal between the hose and tank. Be prepared to catch the small amount of coolant that will spill out.

Pull the tank straight up, it may take a little force as there is a small rubber grommet (red arrow) it sits in on the bottom.
Figure 7

Pull the tank straight up, it may take a little force as there is a small rubber grommet (red arrow) it sits in on the bottom.

Take the old tank to your bench and 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.
Figure 8

Take the old tank to your bench and 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.

Here is the new tank installed.
Figure 9

Here is the new tank installed. I like to install new hose clamps as I find the factory clamps difficult to work with in tight spaces. Do NOT forget to refill the coolant.

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Comments and Suggestions:
Leo Comments: My car is leaking oil from the passenger side oil cooler the hose above the bottom one on the passenger side . What do I need to do to fix it? I just changed the radiator btw does it take a seal ?
October 4, 2016
  Followup from the Pelican Staff: Replace the cooler an the connecting hose. - Nick at Pelican Parts  
Al Comments: I want to replace the coolant in my '05 E320, and this article only goes up to model year 2004. Is the drain plug and draining old coolant pretty much the same set up for an '05? Thanks.
September 29, 2015
  Followup from the Pelican Staff:
The drain for the radiator is on the left side of the radiator, bottom. The block drain is on the right side of the crankcase.

I would grab a repair manual. It will have the procedure, special tools and torque specs.

Give our parts specialists a call at 1-888-280-7799. - Nick at Pelican Parts
 
Hallee Comments: I have replaced the tank because it was old, yello and leaking. The new OEM tank on shows no leaks, and no leaking from hoses. But the coolant level is lowering slowly with driving. There is splattering around the cap. Is the cap supposed to seal tightly or vent to allow for expansion? Do I need a new cap?
January 18, 2015
  Followup from the Pelican Staff: The cap should seal. Only venting when cooling system pressure is too high. I would test the cap with a pressure tester.- Nick at Pelican Parts  
cwmffrwd Comments: Excellent explanation and detailed photos! I had a real problem when unbeknown to me my expansion cap on my CLK 270CDI had disintegrated. Several parts then fell into the tank when I unscrewed the cap. In only 40 minutes I had the tank off and on again and all the parts retrieved and accounted for. Many thanks
July 11, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
lourance Comments: my c240 i allready change tank thermostat and coolint and new compressour and stell no cool from ac your suggistion becouse i am living in saudi arabia middle east and the car is 2001 m112 w203

ac not cool the tech shope tell need to change compressour andrefial ferion idid and no benefet your advice car is C240w203 2001 modile and one quastion more if the ferion not oreginal te china or the same like houndai yoused what defferent
August 29, 2013
  Followup from the Pelican Staff: Have you checked A/C system pressure and compressor activation? When you activate the A/C, the compressor should kick on. If it doesn't, the refrigerant charge may be low. - Nick at Pelican Parts  
frac Comments: this might help too... it's just taken from farther back...
July 1, 2013
  Followup from the Pelican Staff: That is the thermostat housing.
Mercedes EPC has been down all day, or I would give you a part number.
You can try sales, but have your VIN# at hand when you call.
United States and Canada 1-888-280-7799
International customers 1-310-626-8765
-whunter-
 
frac Comments: Here is a photo of the part that I am talking about...
July 1, 2013
  Followup from the Pelican Staff: That is the thermostat housing.
Mercedes EPC has been down all day, or I would give you a part number.
You can try sales, but have your VIN# at hand when you call.
United States and Canada 1-888-280-7799
International customers 1-310-626-8765
-whunter-
 
Frac Comments: Daniel,

Thank you for the info. I was able to get the coolant hose. However, if you fill me in on how many clamps I'll need i'm guessing 2 for the small line..what size exactly, and 4 for the other 2 larger ones.
Also, were you able to figure out the part number for the the splitter that goes from the front of the engine block and connects to the 2 other hoses?
Thanks again.

I can take a picture up close now that I got the car back after the rebuilt tranny.
June 30, 2013
  Followup from the Pelican Staff: Generic worm gear clamps, all auto parts stores have them.
Without a picture, I have no idea what splitter you are asking for.
-whunter-
 
FRAC Comments: I just had my tranny replaced at 197k miles rebuilt w/ updated parts on my 2003 E 320... Attached is the list of items I need to fix the leak in the cooling system JB weld has been holding the low pressure overflow valve for about 6 months now!.
I think that the Behr P/N #: 211 500 00 49 M6 will be sufficient. Does this come with the reservoir cap? I just bought a replacement one about a month ago that should be just fine.
I already have coolant... but was suggested to replace the sensor. I know it works still... that's how I knew when to grab some more water.. is this preventative maintenance necessary? Probably... Also I need the low pressure return hose and some clamps, and the hose attachment to the outlet assembly from engine... ikes... JB Weld goop everywhere.
June 28, 2013
  Followup from the Pelican Staff: Glad this diy helped you.

The hoses should be replaced as needed.

MB# 2115000472
http://www.pelicanparts.com/cgi-bin/ksearch/pel_search.cgi?SUPERCAT_FLAG=Y&make=MBZ&please_wait=N&forumid=&threadid=&command=DWsearch&description=2115000472&x=12&y=9

MB# 2115010625
http://www.pelicanparts.com/cgi-bin/ksearch/pel_search.cgi?SUPERCAT_FLAG=Y&make=MBZ&please_wait=N&forumid=&threadid=&command=DWsearch&description=2115010625&x=13&y=8

IMO: The pressure cap should be replaced with the tank.

MB# 2105010615
http://www.pelicanparts.com/cgi-bin/ksearch/pel_search.cgi?SUPERCAT_FLAG=Y&make=MBZ&please_wait=N&forumid=&threadid=&command=DWsearch&description=2105010615&x=11&y=7

The pressure cap does not come with the tank.
The level sensor should transfer from the old tank with no issue.
-whunter-
 

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