Your cooling system is critical to extending the life of your engine. While the engine lubrication system is very important, your cooling system keeps the engine running at the correct temperature while you are driving. If the engine is running a little hot from a bad coolant pump not circulating enough coolant, the oil will start to break down from the additional heat and provide less lubrication. This is known as thermal breakdown of the engine oil. The coolant pump is the heart of the cooling system. It pumps cooled coolant through the cylinder jacket and the heads to control engine temperature. The coolant gets circulated through the block, head, heater system, radiator and finally returns to the coolant pump.

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. Sometimes, you can also see a slight drip coming from the water pump housing itself. These weep holes are cast into the pump housing and allow excess coolant to drain out if it has leaked past the various seals in the pump. The bearing can fail creating a grinding noise or creating free-play in the shaft, also resulting in a coolant leak.

Remember that your car may have been serviced before and had parts replaced with different size fasteners used in the replacement. The sizes of the nuts and bolts we give may be different from what you have so be prepared with different size sockets and wrenches.

Protect your eyes, hands and body from fluids, dust and debris while working on your vehicle. If you're working with the electrical system, disconnect the battery before beginning. Always catch fluids in appropriate containers and properly dispose of any fluid waste. Recycle parts, packaging and fluids when possible. Never work on your vehicle if you feel the task is beyond your ability.

Our vehicle may vary slightly from yours as models do change and evolve, as they grow older. If something seems different, let us know and share your info to help other users. Do you have questions or want to add to the article? Leave a comment below. When leaving a comment, please leave your vehicle information.

In this article, I'll go over the steps involved with replacing the water pump on Mercedes-Benz W211 models with a 6-cylinder engine. Be sure to work with a cool engine and confirm the cooling system lacks pressure before opening the cooling system.

Drain the cooling system. See our tech article on the cooling system draining and filling.

Read the Full Article: [ Ссылка ]

Time: 3 hours
Tab: $150
Tools: Set of sockets :[ Ссылка ] T50 Torx, 10mm, 17mm, E10, E12, :[ Ссылка ]
Applicable Models: Mercedes-Benz W211 (2003-09) :[ Ссылка ]
Parts Required: Water pump :[ Ссылка ], hoses, engine coolant :[ Ссылка ]
Hot Tip: Work with a cool engine
Performance Gain: Car will cool down again
Complementary Modification: Change serpentine belt, radiator hoses

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