My 190E has a nasty squeal whenever the car is running. I originally thought it was the belt tensioner pulley as it had bad bearings but surprisingly it did not fix the noise. I am almost certain the noise is concentrated right above the water pump. The water pump was replaced on it almost a year ago, however the MB brand coolant was not used to refill the system. Could not having used the proper coolant caused the water pump to make noise? Other than the noise, the engine runs at normal operating temperature.

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1992 190E 2.3
150,000 Miles