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Mercedes Coolant Expansion Tank Replacement


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All parts used in these pictorials are available at the diesel parts for sale page


Safety and security tips:

Please remember to recycle all your used fluids at an appropriate recycling center.  Be mindful to not spill or splash fluids on yourself, others or the ground.  Also as a safety tip please remember anytime you are working on, around or under your car, to wear safety glasses and secure the car with wheel stops and approved jack stands!  


Mercedes Coolant Expansion Tank Replacement

Here is a real quick and easy project that anybody can, and should do as the need arises.  The entire project takes maybe 15 minutes and requires very minimal tools.  If you are running around with the factory expansion tank on your turbo diesel, then take a hard look at it.  Being in a hot harsh environment like the engine compartment, the plastic gets discolored and brittle.  That mean cracking and leaking, at usually the most inconvenient time.  This may be one of those "preemptive strike" repairs while its on YOUR time schedule.

So follow along as we install the new expansion tank.



This is the factory tank and it looks fine to the casual observer.  The tank was getting wet along the front area, and the seem that runs around the belly.  Not enough to drip mind you, but it was getting ready to fail.


One of the leaking areas.  This actually was one of the minor leaking areas, but still needed to be addressed.  Don't try to use silicone or JB Weld on it.  The tank gets to  radiator temp and pressure, and needs to be in good safe working order.



Start by working on a cold car.  DO NOT do this if the engine is at operating temp or you could get badly burned! 

Remove the cap....


Then remove the overflow hose....


Then remove the hose going to the top of the radiator.  This is how the coolant gets from the radiator to the expansion tank.


Now we drain the radiator.  Remove the plastic plug from the bottom of the radiator, and drain into a suitable container.  I do this in a clean drain pan that I only use for coolant.  Don't let any pets near the coolant, they drink and then they DIE!


Let the coolant drain into the pan.  I filter and then reuse the coolant if it is still in good shape.


After the coolant has drained out of the tank, remove the bolt securing the tank to the bracket.


Then remove the 2 screws holding the back of the tank to the fender well.


Then remove the tank to radiator hose at just the tank.  This is the hose that feeds coolant from the tank, to the radiator.


This is the new tank.  They actually did look like this when they were new.  The dingy brown color of your tank is from age, heat and deterioration.


Now we prepare the expansion tank.

On the diesel models, you will install the plug kit.  This is the connection area that a car would have if it has the "low coolant" sensor.  The plug has an O ring and a large clip to hold it in place.  The plug is VERY hard to get in the tank.




Mount the new tank in the same position as the old tank.  Attaching the hose from the radiator to the tank....



Then bolt the tank to the front bracket.....



Then reattach the 2 screws at the rear of the tank....



Reinstall the overflow hose...



Then the supply hose to the tank....



Wow!  All that is left, is to put the drain plug back in the radiator and refill with coolant.  Don't forget to install the radiator cap and run to operation temp.  Check for leaks and you are done.


That was an easy project!