BMW X5: Performance Controls

Cooling System

The cooling system of the N54 engine consists of a radiator circuit and an isolated oil cooling circuit. The fact that there is an isolated oil-cooling circuit ensures that heat is not introduced via the engine oil into the engine's coolant system.

Fig. 71: Identifying Cooling System Diagram

There is a significantly greater quantity of heat on account of this engine's increased power of 75.5 kW/l in comparison with other 3-liter spark-ignition engines.

This boundary condition is satisfied by the engine cooling system with its increased performance. This increase in power was to be realized in spite of some factors less advantageous to cooling.

Factors to be mentioned here are:

• Approximately 15% less flow area is available on account of the intercooler located below the radiator.
• The already small amount of space provided by the engine compartment is further limited by the accommodation of further components.
• Because the exhaust turbochargers are cooled by the coolant, an additional quantity of heat is introduced into the system via these turbochargers.

Measures for increasing cooling-system performance:

• Coolant pump with increased power - 400 W/9000 l/h
• Separation of water and engine-oil cooling
• Radiator with increased power
• Electric fan with increased power 600W for all gearbox variants

The structure of the coolant circuit is the same as that of the N52 engine. The engine is flushed through with coolant in accordance with the cross-flow concept. Cooling output can be influenced as a function of load by activating the following components:

• Electric fan
• Electric coolant pump
• Map thermostat

It is also possible that an N54 engine equipped with an automatic gearbox to utilize the lower area of the radiator to cool the gearbox by means of the gearbox oil cooler. This is achieved as in the N52 engine with control sleeves, which are introduced into the radiator tank.

Engine-oil Cooling

The N54 engine is equipped with a high-performance engine oil cooler. The pendulum slide pump delivers the oil from the oil sump to the oil filter. A thermostat flanged to the oil filter housing admits the oil to the engine-oil cooler. The engine oil cooler is located in the right wheel arch in the E92. The thermostat can reduce the resistance opposing the oil by opening the bypass line between the feed and return lines of the engine oil cooler.

This ensures that the engine warms up safely and quickly.

Radiator

Design measures have been used to increase the performance of the radiator itself. The performance of a radiator is dependent on its radiation surface. However, the intercooler location had to be underneath the radiator, and this meant that is was necessary to compensate for the smaller flow area available.

Compared with the N52 engine, the radiator used in the N54 engine has a block depth which has been increased to 32 mm. In addition, the water pipes are situated closer together than in previously used radiators. The upshot of this is an increase in the utilizable radiation surface.

Electric Coolant Pump

The coolant pump of the N54 engine is an electrically driven centrifugal pump with a power output of 400W and a maximum flow rate of 9000 l/h. This represents a significant increase in power of the electric coolant pump used in the N52 engine, which has a power output of 200 W and a maximum flow rate of 7000 l/h.

The power of the electric wet-rotor motor is electronically controlled by the electronic module (3) in the pump.

The electronic module is connected via the bit-serial data interface (BSD) to the MSD80 engine control unit.

The engine control unit uses the engine load, the operating mode and the data from the temperature sensors to calculate the required cooling output.

Based on this data, the engine control unit issues the corresponding command to the electric coolant pump. The electric coolant pump regulates its speed in accordance with this command.

The system coolant flows through the motor of the coolant pump, thus cooling both the motor as well as the electronic module. The coolant lubricates the bearings of the electric coolant pump.

Fig. 72: Identifying Engine-Oil Cooling Diagram

NOTE: The same rules apply to all electric coolant pumps. The pump must be filled with coolant when removed for service to prevent any corrosion. Also, the pump impeller must be turned by hand before installation to ensure the pump is not seized.

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