Modern, low-emission, high-output engines have to run within a very small temperature range in order to maintain their efficiency.
The water pump allows this to happen by regulating the coolant flow according to the demand of the ECU. Furthermore, forced induction engines will require additional cooling of the turbo/supercharger after shutdown in order to prevent premature wear or even damage.
AVOID GETTING TOO HOT
When a turbocharged vehicle is switched off, the temperature of a turbo bearing can reach up to 340°C within seconds. This temperature can cause the oil in the bearing housing to lose viscosity and lubricating properties. This causes the bearing to wear and leads to the failure of any rubber or plastic seals.
When the engine is switched off, the electric pump is designed to continue pumping coolant for a number of minutes. This occurs until the turbo has sufficiently cooled which manages the temperature, prolonging the turbo’s lifespan.
WHAT CAN GO WRONG?
In order to ensure the longevity of a repair job, it is important understand the true causes.
BMW 3, 5 Series, X3, X5 & Z4 with N51, N52 and N52K engine
These vehicles have a tendency to experience water pump failure at around 60k-100k miles.
The issue is not typically a leak or mechanical breakdown. However, it often starts out as a problem with the electric motor in the pump that begins to slow down, eventually coming to a complete stop. Monitored by the primary vehicle control module, it is only detected during a system scan that will read as a water pump speed deviation or loss of communication to the water pump.
If undetected by a system scan, the only warning will be the yellow light illuminating, followed shortly by a red light indicating engine overheat.
DO NOT DRIVE THE VEHICLE IN THIS CONDITION. This can lead to a costly engine replacement/overhaul as a result of heat damage.
Fitted with a primary electric water pump in addition to a traditional belt driven option, a number of drivers have complained that the water pump continues to run long after the set period when the vehicle has been switched off, running the battery flat.
In this case, the water temperature sensor has simply failed and locked open, causing the pump to continuously run.
Range Rover/Range Rover Sport Mk3 (2005-2009)
The wires that go into the electric water pump connector (C3006) may have been wired the wrong way. As a result, the auxiliary coolant pump that cools the supercharger runs backwards. Over time, this degrades the pump and causes it to fail or run very poorly.
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