Cooling System Flow Diagram – N55



1 Radiator

2 Engine oil to air cooler (hot climate version)
3 Heater coil
4 Characteristic map thermostat
5 Electric coolant pump
6 Exhaust turbocharger
7 Heating heat exchanger

8 Coolant valve
9 Oil-to-coolant heat exchanger
10 Coolant temperature sensor
11 Engine oil thermostat (hot climate version)
12 Expansion tank
13 Coolant level switch
14 Equalization line
15 Auxiliary radiator
16 Electric fan

Identifying Cooling System Components – N55

Cooling System Components - N55
A Auxiliary radiator
B Coolant feed line to auxiliary radiator
C Oil-to-coolant heat exchanger
D Coolant feed line to oil-to-coolant heat exchanger
E Coolant return line from auxiliary radiator
1 Zone 1 feed line, heating heat exchanger

2 Zone 2 feed line, heating heat exchanger
3 Coolant valve
4 Expansion tank
5 Equalization line
6 Radiator
7 Bypass line for small cooling circuit
8 Thermostat
9 Electric coolant pump
10 Exhaust turbocharger supply line
11 Thermostat for transmission oil cooling
12 Coolant feed line to engine block
14 Transmission oil-to-coolant heat exchanger
15 Connection, transmission oil line
16 Connection, transmission oil line
17 Return, heating heat exchanger

The following graphic shows the connection of the auxiliary radiator to the cooling system. The auxiliary
radiator is connected to the radiator by means of parallel coolant lines, thus increasing the cooling surface area.
This system is combined with an oil-to-coolant heat exchanger mounted on the oil filter housing. (See in the previous graphic.)

Identifying Auxiliary Radiator Components – N55

Auxiliary Radiator Components - N55
1 Radiator
2 Auxiliary Radiator
3 Feed connection to the auxiliary radiator
4 Feed connection at the auxiliary radiator
5 Return connection to the auxiliary radiator
6 Return connection from the auxiliary radiator
NOTE:If a separate oil to air cooler is not installed, an auxiliary radiator in conjunction
with an oil to coolant heat exchanger is used to cool the engine oil.

Identifying Engine Oil Cooling Components (Hot Climate) – N55

Engine Oil Cooling Components (Hot Climate) - N55

1 Oil filter module
2 Thermostat
3 Oil cooler lines
4 Engine oil to air heat exchanger (oil cooler)

NOTE: Most current US vehicles use a separate engine oil to air heat exchanger to cool
the engine oil (hot climate version).

Coolant Passages
The coolant passages in the cylinder head are also used for indirect cooling of the fuel injectors. The following graphic clearly shows that the coolant flows over the valves and the fuel injectors, thus reducing the heat transfer to the components to a minimum.

Casting Of Coolant Passages In Cylinder Head – N55

Coolant Passages In Cylinder Head - N55
1 Channel, intake valves
2 Channel, fuel injectors
3 Channel, exhaust valves
4 Connection, coolant hose to thermostat (small cooling circuit)
5 Connection, coolant hose to radiator (large cooling circuit)

The cast iron cylinder liners are cast into the aluminum die-casting. The deck area (webs) between the cylinders have grooved coolant passages. Coolant can flow along these grooves from one side of the block to the other, thus cooling the deck area between the cylinders.

Identifying Coolant Passages And Web Cooling Of Engine Block -N55

Coolant Passages And Web Cooling Of Engine Block

1 Cooling duct
2 Cylinder liner
3 Grooved coolant passage
4 Oil return ducts, exhaust side
5 Oil return ducts, intake side

2011 BMW 535xi ENGINE N55 – Service Information

2011 BMW 535xi ENGINE N55



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