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Pelican Technical Article:

Coolant Expansion Tank Replacement

Jared Fenton

Time:

1 hour1 hr

Tab:

$45

Talent:

***

Tools:

10mm socket, pliers, screwdrivers

Applicable Models:

Mercedes-Benz W210 (1996-03)

Parts Required:

New expansion tank

Hot Tip:

Replace the tank with the engine COLD

Performance Gain:

A major cooling system leak fixed.

Complementary Modification:

Flush cooling system

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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 30 minutes.

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.

The first step in replacing the old coolant tank is to remove the airbox from the car. Please refer to our article on changing your air filter for more info. Once the upper airbox and filter are removed, pull the lower airbox straight up and out of the engine compartment. This will give you access to remove the coolant tank.

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.

You might want to wait overnight to make sure that the coolant is not hot. If you open the coolant tank with the car warmed up, it could burn you. There is heat and pressure in the system. When you are sure that the coolant is not hot, remove the cap and use either a turkey baster or a large syringe to siphon the coolant out of the tank. You'll want to keep siphoning until the level is just at the bottom of the tank. This prevents spilling coolant all over the ground when you remove the tank. Keep in mind that when you remove the tank from the engine compartment, the level will drain back down through the bottom hose.

To the side of the coolant filler cap, you will see a 10mm nut holding the tank to the inner fender. Remove the nut and pull the old tank straight up to release the tabs holding it in the mounting bracket down near the headlight assembly. Rotate the tank over to gain access to the coolant level sensor. Squeeze the tabs on the electrical connector to unplug it from the coolant level sensor. Now rotate the coolant level sensor to release it from the old tank. Also pull off the vent hose at the collar of the filler neck.

Next use a pair of pliers to remove the hose clamp on the upper hose connection and pull the hose off. You may want to carefully take a small screwdriver and work it between the hose and the tank connection. Coolant hoses sometimes stick to these connections and have to be 'worked' loose. Just carefully work all the way around it and pull it off. Once free, pull the tank up. This will drain the remaining coolant back into the bottom line. Now locate the lower hose and loosen the hose clamp securing it to the tank. Again, carefully work the lower hose free if it's stuck. With the tank removed, clean around the area where it has been leaking if there is any baked-on coolant.

Fit the coolant level sensor to the new coolant tank. It can only fit in one way, once it has seated, rotate the sensor to lock it in place. Take the new tank back over to the car and plug in the electrical connection to the sensor, making note of which way it plugs in.

Slide the lower hose over the fitting on the bottom of the tank and re-fit the hose clamp. Also slide the overflow hose onto the nipple on the filler neck of the new tank. Carefully maneuver the new tank into place, making sure that the tabs on the lower edge fit into the rubber grommets on the inner fender. Give it a good push as you also maneuver the bracket at the top over the mounting stud.

Re-fit the upper 10mm nut and tighten it. Slide the upper hose connection on and re-fit the hose clamp. Now, fill the tank with coolant until it registers in-between the MIN and MAX lines molded into the tank. Start the car and let it warm up. Now recheck the level and add coolant if it has dropped. Install the cap on the new tank and that's it!

Shown here is a new coolant expansion tank with cap for the Mercedes E320 (W210).
Figure 1

Shown here is a new coolant expansion tank with cap for the Mercedes E320 (W210). It's a good idea to replace the tank if you notice any coolant leaking from the seams of the old one.

The first step in replacing the old coolant tank is to remove the airbox from the car.
Figure 2

The first step in replacing the old coolant tank is to remove the airbox from the car. Please refer to our article on changing your air filter for more info. Once the upper airbox and filter are removed, pull the lower airbox straight up and out of the engine compartment. This will give you access to remove the coolant tank.

Here is a close-up shot of the 10mm nut that secures the tank to the inner fender (green arrow).
Figure 3

Here is a close-up shot of the 10mm nut that secures the tank to the inner fender (green arrow). Now use a turkey baster or syringe to siphon as much coolant as you can out of the old tank. This prevents spilling coolant all over the ground when you remove the tank. Keep in mind that when you remove the tank from the engine compartment, the level will drain back down through the bottom hose. Remove the 10mm nut and pull the old tank straight up to release the tabs holding it in the mounting bracket down near the headlight assembly.

Next use a pair of pliers to remove the hose clamp on the upper hose connection and pull the hose off (green arrow).
Figure 4

Next use a pair of pliers to remove the hose clamp on the upper hose connection and pull the hose off (green arrow). At the bottom of the tank, squeeze the tabs on the electrical connector to unplug it from the coolant level sensor (purple arrow). Rotate the coolant level sensor to release it from the old tank.

Now rotate the tank over to loosen the hose clamp holding the lower hose to the tank.
Figure 5

Now rotate the tank over to loosen the hose clamp holding the lower hose to the tank.

Fit the coolant level sensor to the new coolant tank.
Figure 6

Fit the coolant level sensor to the new coolant tank. It can only fit in one way, when it has fully seated, rotate the sensor to lock it in place.

Connect the bottom hose to the bottom of the new tank and slide the hose clamp back on.
Figure 7

Connect the bottom hose to the bottom of the new tank and slide the hose clamp back on. Maneuver the new coolant tank into place, making sure that the two tabs on the lower edge fit into the rubber grommets on the inner fender. Give it a good push as you also maneuver the bracket at the top over the mounting stud. It will take a little effort to get the tank in as its a tight fit. Re-fit the upper hose connection and install the 10mm nut holding the tank to the bracket. Once in place, fill the tank with coolant until it registers between the MIN and the MAX marks.

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Comments and Suggestions:
Jonas Comments: I got problem with the coolant is coming up on my display and says that coolant is low but i think it is a sensor because allways when my washer fluid run out then its low coolant coming up on the display
March 27, 2014
  Followup from the Pelican Staff: I would use your owners manual to confirm what light it is Then adjust the fluid the light pertains to. - Nick at Pelican Parts  
Beck Comments: Thanks this was really helpful
February 3, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Rod Comments: Where is a heater core located in 97 Mercedes E300D ??? And where it may leak the coolant???
December 18, 2013
  Followup from the Pelican Staff: If I remember correctly, it is mounted behind the dashboard, in the heater box, centered. It would leak coolant out of the heater box drain and possibly onto the floor of the vehicle interior. - Nick at Pelican Parts  
Rod Comments: It is coolant, where is it coming out and how to fix it??? Thanks, Rod
December 10, 2013
  Followup from the Pelican Staff: You will have to look the vehicle over and locate the area the coolant is leaking from. - Nick at Pelican Parts  
rod Comments: very good, i have a coolant leak somewhere in front of passenger side just above footrest, where is that coming
from??? Please help, thanks.
Rod
December 9, 2013
  Followup from the Pelican Staff: Take some of it and smell it. You need to figure out if it is coolant (from the heater core) or rain water (from the interior air intake). - Nick at Pelican Parts  

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Page last updated: Thu 10/2/2014 12:41:56 AM