Cooling System
Cooling System
The (E85) Z4 cooling system is similar to the E46 with the exception of the following changes:
^ Cooling module (viscous fan eliminated)
^ Air-controlled IHKA system (water valves eliminated)
^ Use of Electric Power Steering (power steering cooler eliminated)
Cooling Module
The (E85) Z4 cooling system uses a cooling module similar to the E46.
On the (E85)Z4) Z4, the cooling module is separated by a partition (radiator core support) from the engine.
1. Partition (structural/core support)
2. Cooling module
The cooling module contains the following cooling system components:
1. Cooling radiator
2. Coolant expansion/reservoir tank
3. Air conditioning condenser
4. Electric fan (suction or puller type)
^ Automatic transmission fluid radiator (only if equipped)
Coolant Expansion Tank
When filling the coolant expansion tank, the engine can be almost completely filled with coolant and self bled. The heater core return flows directly into the coolant expansion tank.
This prevents air pockets in the heating system and ensures trouble-free bleeding of the cooling system.
Principle of Operation
Cooling System Function
The concept of the cooling system in the (E85) Z4 M54 ensures high coolant temperature in the crankcase which reduces the friction between cylinder walls and pistons, reducing fuel consumption. The increase of coolant temperature in the crankcase is achieved by flowing the coolant mainly through the cylinder head.
A low coolant temperature in the cylinder head has a positive effect on the entire torque characteristics of the engine: Low temperatures in the cylinder head lead to a high engine charge (air and fuel) and a rise in the anti-knock limit. In addition, a low coolant temperature in the cylinder head improves the durability of the components. This concept is referred to as the partial engine flow cooling concept (MTK).The coolant is fed by the water pump via a cast-on feed duct to the rear end of the cylinder head and from there towards the front to the coolant outlet (radiator outlet if engine warmed up). The water jacket in the crankcase is connected to the flow in the cylinder head via bore holes in the crankcase and through the cylinder head gasket. This means that only a part volume of the coolant flows through the crankcase.
The MTK principle leads to a significant temperature increase in the crankcase with virtually unchanged temperature in the cylinder head.
Map-controlled Thermostat
The effect of the MTK cooling concept is additionally supported in the M54 by control of the coolant temperature using the map thermostat. With low load, the map thermostat sets a high coolant temperature that has a favorable effect on fuel consumption. At full load and/or high engine speed, the coolant temperature is lowered to protect the components.