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.

Replacing the water or coolant pump on W203 is certainly a doable job for a DIY'er but it is not a quick job. If this is one of the first projects you are attempting on your car, give yourself at least five hours to get the job done and don't forget to refill the coolant.

There are several things that will need to come off or out of the car to replace your water pump including the air filter ducts, engine cover, fan and you will need to drain the coolant as well. This is also a very good time to replace your hoses if they are getting on in age.

Please see our articles on replacing your air filter to remove the ducts and cover. Please see our article on replacing your fan to remove the fan and please see our article on replacing your radiator hoses to drain your radiator.

This article begins at the point that you have completed all the other work to get to this point.

You are going to remove the Poly-V belt to remove the coolant pump as well as remove the idle pulley. Inspect your belt and replace as needed. With an E10 (reverse Torx socket) and driver locate the tensioner and using the Torx driver turn it counter-clockwise 45 degrees. You can now slip the belt off the tensioner. You can also lock the tensioner into the open position if you need both hands to install the new belt. Turn the tensioner all the way counter-clockwise and insert a retaining pin between the rotating part and the tensioner base. If you do not have a retaining pin you can use a 5mm Allen key.

To remove the coolant pump you will first need to remove the idle pulley which is located right above the coolant pump pulley. Insert a flathead screwdriver between the cover plate and the pulley and gently pry the plate off. With the plate off use a T-50 Torx and remove the pulley bolt. The bolt is extra long so make sure to label it as it is not easy to replace if you loose it.

Move to the two hoses that connect to the lower part of the coolant pump. Remove the hose that goes to the auxiliary coolant pump from the clip that holds it to the alternator bracket. Next using a flat head screwdriver, remove both hoses. You may need to run the screwdriver between the hoses and housing to help break any seal that has developed.

Two of the bolts that hold the pump in place also hold the bracket for air pump check valve. Use an E10 and remove these two bolts first and then zip tie the bracket out of the way.

Remove the electrical connection for the coolant temperature sensor as you do not damage it while removing the pump.

Next, remove all the bolts that hold the pump to the engine including the one that supports the alternator.

There are one E14, four E12 and twelve E10 bolts connecting the coolant pump to the engine and most of them are different lengths. I like to take an old cardboard box and draw an outline of the pump on it, as I remove each bolt I stick it in the cardboard where came off so I will know where to put it back when I put the new pump on.

Remove the old pump and inspect it for damage.

Remember to replace the gasket whether you are installing a new pump or putting the old one back on.

Installation is the reverse of removal and don't forget to fill up the system with coolant

Note: If you have not read the article and just like to use the pictures to help you, there are several procedures you need to perform before getting to this point, please refer to the article for the steps needed to get to this far.

Read the Full Article: [ Ссылка ]

Time: 4 hours
Tab: $110
Tools: 8mm socket, E10, E12, E14, T-50 Torx driver, flathead screwdriver
Parts Required: New water pump and gasket:[ Ссылка ]
Hot Tip: Keep track of where the bolts go
Performance Gain: Properly cooled engine
Complementary Modification: Replace your radiator hoses

Applicable Models:[ Ссылка ]
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)

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