Common water pump problems are seal leakage and breaking of the shaft or casings. When coolant leaks out of the pump's weep hole, looks rusty and leaves behind rust and calcium deposits, the cooling system has been contaminated due to improper pressurization. Bearing overload is the typical cause of a broken shaft, identified by a clean fracture, usually in the front portion of the shaft. Breaks in the casings, typically occurring around the bearing support, are caused by excessive vibration.
Lack of proper pressurization of the cooling system allows air to enter the system and rust to build up. The abrasiveness of rust and other minerals in the water passing through the pump wear away the pump seal, causing leakage. This problem requires replacement of the water pump after the contaminated system has been thoroughly flushed. In locations where water contains a high percentage of minerals, using distilled water in the pump is recommended, along with regular maintenance.
Water pump shafts break when the bearing is overloaded due to vibration or imbalance, which also causes casing breakage. If the shaft shows no discoloration, then the cause was sudden and exacerbated by rapid acceleration of the engine. If blue discoloration is present, the overload was gradual and most likely caused by excessive heat over a period of time. Corrective actions in response to both shaft and casing breakage include careful alignment of the pulleys and inspection of the fan and fan clutch assembly for fan damage, a worn spacer, or worn or damaged fan clutch.