In the first part of the entry of Thermal management I already mentioned, that the cooling system of modern N series engines has following (powerful) tools:

  • electrical fan with management, power – several hundreds of W;
  • electrical water pump with management, power – 400 .. 700 W;
  • controlled thermostat.


However, if by some reason these tools cannot handle the cooling of the engine, some additional measures are available.

In the image: the action of the DME, when the increased temperature of the cooling agent is detected.

As we can see, additionally the power of the air conditioner is decreased, the power of the engine is decreased even to 10 % of the initial one!


Now I will tell a bit from my observations, how the modern engines are managing the cooling system.

Management of cooling system is RADICALLY different from simply “let’s maintain temperature X”!


How are the modern BMW engines managing the cooling system?

DME knows, how much fuel is burned, it knows the efficiency of the engine. Accordingly – DME knows, how much energy in the current moment is converted to the heat (not in torque) – all this heat has to be released into the atmosphere. Accordingly – DME doesn’t wait until the engine block will heat up. DME cools it down immediately – as soon as the driver touches the accelerator pedal. Moreover, this model has the following “features”:

  • DME takes into account the differences in the efficiency of different modes (for example, for N43/N53 engines – Homogeneous vs Stratified);
  • DME takes in account thermal capacity (inertia) of piston groups – based on special curves, it apprehends decreasing of the water pump flowrate to avoid local overheating;
  • the minimal flowrate of water pump is limited to avoid too high-temperature differences in different sectors of the engine and local boiling of the cooling agent;
  • if the required torque of the engine is rapidly increased, DME immediately switches from Normal/ECO to High power mode. To speed up this process, the flowrate of the water pump is significantly increased (to 100 %) and the opening of the thermostat is forced (heating it up to 100 %). To avoid the possibility of local overheating, the minimal power of the water pump is increased to 40 %.


DME create adaptation maps for the water pump, electrical fan, radiator, thermostat and it’s heating hubs. DME regularly tests the performance of these hubs.

For example:

  • driving evenly, with electrical fan practically turned off (its minimal PWM is 7 %), without heating of the thermostat the power of the water pump varies (its minimal power in Normal/ECO mode is 15 %), checking, whit what power the thermal balance is reached;
  • driving evenly, with electro fan turned off, keeping unchanged flowrate of the water pump, the heating os the thermostat is changed and the impact of it is evaluated;
  • in idle, the efficiency of the electrical fan (and cooling radiator) is evaluated;
  • in idle, the engine’s ability to maintain lowered temperature (Mapped mode with 80 oC) is evaluated;
  • in idle, the performance of the thermostat and its heating is evaluated, managing them in the engine’s heating stage;
  • in idle, the performance of the water pump is evaluated: thermostat is heated for 100 %, the radiator is cooled down with 80 % of power, changing the flowrate of the water pump, according to the exact heating map, the 90 oC is reached.

I think this is only a part of the test tasks of the thermal management. Unfortunately, I don’t have any description of algorithm/functionality.

One more interesting nuance: if DME detects signs of overheating of the engine (at least once the yellow warning sign lighted up in the KOMBI), in the problematic segment DME turns on Mapped mode and checks availability to maintain it. Accordingly – DME doesn’t allow the situation to become problematic. Only, when DME will get confirmation  for several times (not less than 3 .. 5 cycles in case of single/medium overheating), that the cooling of the engine is in good condition (it means, the overheating problem is eliminated), DME will restore other (High power, Normal) modes. ECO mode (as a mode with the highest temperature) will be restored only after a long time.


For example, if the engine has overheated in idle mode (yellow warning sign will light up in the KOMBI):

  • in this sector, (idle) DME will maintain Mapped mode (80 oC). If several times in a row maintaining of this mode will succeed (it means, the heating of the thermostat will be less than 100 %; the power of the electric fan – less than 90%; the power of the water pump – below 50 %), the engine will perform next tests;
  • will check the flowrate map of the water pump increasing the temperature to 90 oC according to the exact timetable (changing the flowrate of pump, the thermostat is heated by 100 %), will check the heating of the thermostat; efficiency of the electrical fan.

Only after successful completion of these tests, DME will restore Normal mode in idle. ECO will have to wait for a longer time. Taking in account, that for confirmation of the tests at least 15 .. 20 minutes are required, you can not hope for rapid restoring of the full functionality of the engine after overheating!

Moreover, take in account, that:

  • in case of moderate overheating of the engine no error messages will be recorded;
  • diagnostic tools (INPA/ISTA) have no learnbits, indications, in which mode the thermal management works;
  • even deleting of adaptations don’t restore full functionality mode – DME will perform all tests by itself, to make sure, then the cooling of the engine performs its functions.


Taking into account everything, mentioned before, we have to make a conclusion – if the engine has a periodical tendency to overheat, it will work with reduced temperature; fuel consumption will increase.

Diagnostics of overheating problems is complicated because there are no error messages, no status bits, which would indicate emergency mode.


A sample of diagnostics

N53B30. Complaints – in hot weather (when the outside temperature is at least 25 oC) observed:

  • the power of the engine, driving in traffic jams, is decreased;
  • the air conditioner doesn’t cool down in these conditions;
  • the electrical fan works very loudly.


For diagnostics reasons, the car was left to work in idle for a longer time. After 20 minutes KOMBI lights up the yellow warning sign regarding overheating of the engine, on the display of CCC – appropriate inquiry to reduce the load of the engine. As the engine works in idle, obviously, it’s not possible to reduce its load (and the heating was not caused by too aggressive driving).

INPA connection displayed following data:


  • oil temperature: 122 .. 124 oC
  • engine temperature: 123 .. 124 oC


  • power of cooling fan: 91 %


  • heating of the thermostat: 100 %


  • inquired power of water pump: 52 %.


What do these data mean?

  • thermostat, heated for 100 %: DME tries to open it as max as possible, to increase the flow of the cooling agent to the radiator;
  • 52 % power of water pump in idle – practically max value for this mode;
  • 91 % of electrical fan – ventilator tries to cool down the radiator with max power.


Nevertheless, all techniques are taken, the temperature of the cooling agent and the engine didn’t drop.

Opening the engine hood, it was found:

  • the cooling fan blows very hot air (it means – the cooling agent gets to the radiator; the thermostat is open, the water pump pumps the cooling agent);
  • the flow of the hot air is weak, although the cooling motor turns in high speed.


Conclusion: the radiator was clogged.

The washing of the radiator was performed with Karcher high-pressure washer. After washing, the residues of sand and mud were clearly visible on the protection panel of the car – they were the reason for low air flow.


Turning on the engine after washing, DME thoroughly checked the ability of the engine cooling system to cool down the engine. DME turned on Mapped mode (with target temperature 80 oC) and the thermal balance was reached by following parameters:

  • heating of the thermostat: 80 .. 90 %
  • power of the water pump: 35 .. 40 %
  • power of the fan: 50 .. 70 %

As you see, all three “arguments” for cooling the engine are used on partial power, it means, they had a power reserve. Moreover, you have to take into account, that this time the temperature of 80 oC was maintained – it’s for 44 (!) degrees lower than previously (in addition, previously: by full heating of the water pump and thermostat, 91% of power of electrical fan, the thermal balance was not reached)!


This result was very satisfying both for me as the performer of the diagnostics and also for DME. After performing 3 .. 5 such cooling cycles, DME allowed Normal mode for idle.

After cleaning the radiator, the engine has full torque also when the outside temperature is 32 oC, also the AC works as it has to.


And finally – typical parameters of N43/N53 engines, driving evenly with 80 .. 100 km/h.

Normal/ECO mode (105/112 oC):

  • electrical fan: 7 %
  • heating of the thermostat: 0 %
  • waterpump: 15 .. 30 % (min = 15 %)

High power mode (95 oC):

  • electrical fan: 7 % (min)
  • heating of the thermostat 0 .. 100 % (>0, switching from Normal to High power)
  • waterpump: 40 .. 100 % (min = 40 %)


Related entries:

Thermal management of N series engines

Engine temperature. Hidden menu

Electric waterpump