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Pelican Technical Article:

Coolant Pump Replacement

Steve Vernon

Time:

3 hours3 hrs

Tab:

$100 to $500

Talent:

***

Tools:

E12, E10 Torx, 17mm socket, flathead screwdriver

Applicable Models:

Mercedes-Benz C350 (2007-14)
Mercedes-Benz CLK350 (2006-09)
Mercedes-Benz E350 (2006-14)
Mercedes-Benz GLK350 (2010-12)
Mercedes-Benz ML350 (2006-14)
Mercedes-Benz R350 (2006-12)
Mercedes-Benz S350 (2006, 2012-13)
Mercedes-Benz SLK350 (2005-14)

Parts Required:

New water pump and gasket

Hot Tip:

Keep track of where the bolts go

Performance Gain:

Properly cooled engine

Complementary Modification:

Replace your radiator hoses

When a water pump begins to fail, you'll notice that the car tends to overheat at low engine speed, such as sitting at a stoplight. When you accelerate, the engine temperature will drop. Now, this is not always indicative of a water pump, but a good starting point. You may also want to try squeezing the top radiator hose with the engine warmed up and running. You should feel pressure build up on the back of the hose and surge once it is released. If you feel no pressure, it's a fair bet that the water pump is failing.

You are going to need to drain the coolant to replace the water pump. New coolants can last a long time so if your coolant is good there is no need to replace it. Just make sure you drain it into a clean container and you can reuse it. If your coolant is old or failing this would be a good time to give the system a flush. Please see our article on draining and flushing your coolant system.

Replacing the water or coolant pump on the W204 is certainly a doable job for a DIY'er but if this is one of the first projects you are attempting on your car, give yourself at least four hours to get the job done. Don't forget to refill and bleed the coolant.

You need to remove the front engine cover (red arrow) and the air ducts (yellow arrows) to replace the coolant hoses so please see our article on engine cover removal for additional assistance.
Figure 1

You need to remove the front engine cover (red arrow) and the air ducts (yellow arrows) to replace the coolant hoses so please see our article on engine cover removal for additional assistance.

Next, you need to remove the under body trays and drain the radiator (red arrow).
Figure 2

Next, you need to remove the under body trays and drain the radiator (red arrow). Please see our article on these procedures for further assistance.

Remove the drive belt by placing a 17mm socket on the tensioner and turning it counter clockwise then slipping the belt off (red arrow).
Figure 3

Remove the drive belt by placing a 17mm socket on the tensioner and turning it counter clockwise then slipping the belt off (red arrow). If you need more help including a picture on the routing of the belt for installation please see our article on drive belt replacement.

You are going to be working with E-Torx bolts.
Figure 4

You are going to be working with E-Torx bolts. Make sure you have the right sockets and E-Torx sockets, and do not try and remove the hardware with something else.

There are two idler pulleys attached to the water pump that you will need to remove to access the water pump mounting bolts.
Figure 5

There are two idler pulleys attached to the water pump that you will need to remove to access the water pump mounting bolts. Use a T10 Torx and remove the single bolt and the smooth pulley (red arrow).

Next use a T12 socket and remove the single bolt and ridged pulley (red arrow).
Figure 6

Next use a T12 socket and remove the single bolt and ridged pulley (red arrow).

Remove the lower right side hose from the water pump by using a flathead screwdriver and releasing the quick release clip and pulling the hose out from the pump (red arrow).
Figure 7

Remove the lower right side hose from the water pump by using a flathead screwdriver and releasing the quick release clip and pulling the hose out from the pump (red arrow). Even though you have drained the radiator be prepared for some coolant to spill out.

You can now remove the water pump (red arrows).
Figure 8

You can now remove the water pump (red arrows). There are several different size and length of fasteners on the pump so be prepared to keep track of them as you remove them.

There are two sizes of bolts used to secure the pump.
Figure 9

There are two sizes of bolts used to secure the pump. With the pump off this photo illustrates the location of the E10 Torx bolts (yellow arrows) and E12 Torx bolts (red arrows).

Drawing a quick outline of the pump also helps to keep track of what hardware goes where, because not only are they different size heads there are different lengths.
Figure 10

Drawing a quick outline of the pump also helps to keep track of what hardware goes where, because not only are they different size heads there are different lengths.

With all the bolts removed the pump will come off easily along with the gasket (red arrow).
Figure 11

With all the bolts removed the pump will come off easily along with the gasket (red arrow).

The gasket is constructed of metal so they tend to not stick to the surface of the pump and engine case like old type gaskets.
Figure 12

The gasket is constructed of metal so they tend to not stick to the surface of the pump and engine case like old type gaskets. Always install a new gasket every time you remove the pump.

You need to thoroughly clean the mounting surface before you install the new pump and gasket (red arrow).
Figure 13

You need to thoroughly clean the mounting surface before you install the new pump and gasket (red arrow). Use something soft, like a plastic trim tool or a Scotch-Brite pad to clean this area. Never use a razor or anything that could gouge the surface. Installation is the reverse of removal. Do NOT forget to refill and bleed the coolant.



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