When cold weather comes, lowered temperature of the engine is very common appearance. Due to this, the fuel consumption increases. CO catalytic converters are damaged (due to overheating), other problems are possible. In this entry – about BMW petrol engine problems.


At first – very often mistakes are made when indicating the engine temperature. Modern engines have several temperatures of liquids, which are displayed by diagnostics tools:

  • oil temperature;
  • coolant temperature, output;
  • coolant temperature, after cooling radiator;
  • engine temperature.

Additionally DME measures: inlet air temperature, the temperature of the engine in the moment of start, the temperature of DME management unit, exhaust temperature (N43/N53), etc. In all these data you can easily get mistaken.


Important parameter: engine temperature!


Second: KOMBI hidden menu can display not the engine, but the coolant liquid temperature! So at first use INPA or ISTA D/+ to clarify, which temperature exactly is displayed by a hidden menu of KOMBi of your car. How to do it, is described here.


Third: temperatures of engine and coolant can differ (usually are different) for 5 .. 10 oC! Usually, the temperature of the coolant is lower.


Fourth: temperature indicator for IKE/KOM (for older vehicles, who have it) will be in the middle position when the engine temperature is 90 +/-15 oC. Accordingly – we CAN NOT correctly evaluate the temperature of the engine, using only this indicator! Even by 75 oC the arrow will be in the middle position!


Collecting all, mentioned before, we have to take into account following:

  • can not use IKE/KOM indicators to control the temperature;
  • can not use KOMBI hidden menu – at first have to clarify, exactly which temperature is displayed in this menu;
  • checking the data in INPA/ISTA D, have to follow carefully, exactly which temperature is displayed.


If you follow all preconditions, but it’s completely clear, that the temperature of the engine is lowered (below 90 oC).


Significant nuance: BMW engines, starting with M62; M52TU (M54) have thermostats, which are equipped with heating. Thanks to this heating, the temperature of thermostat opening can be lowered.


In the image: structure of thermostat with heating.

Opening temperature of thermostat opening is lowered:

  • during warming-up of an engine, to reduce the temperature difference between oil and coolant;
  • in cases, when the oil quality/temperature/level sensor is damaged;
  • N series engines: if by some reason the engine maintains Mapped mode (80 oC).


N series engines can work in four different temperature modes, more about it you can read here.

Mapped mode (80 oC) is turned on (in addition to previously mentioned):

  • if the engine works in idle for a longer time;
  • if DME has detected decreased oil pressure by higher engine temperature;
  • if DME has detected insufficient performance of CO catalytic converters;
  • if the engine management system performs tests of thermal management performance;
  • if the engine management system has previously detected inadequacy in thermal management performance.


The engine management systems of N series engines regularly measure the performance of the following components:

  • cooling radiator (efficiency);
  • thermostat (with or without heating);
  • the curve of thermostat heating;
  • water-pump (flow-rate by different required values).


Note: even in situations, when all elements of the cooling system work correctly, DME regularly (every after a certain time) performs their performance check. During these tests as if by visible reason Mapped mode (with lowered temperature: 80 oC) is turned on for some time. In this case – this is a normal situation, no need to worry.

If DME has detected incorrect performance of any of elements (result: increased or lowered temperature), in these engine conditions DME turns on the Mapped mode (engine temperature: 80 oC).

After eliminating the problem (for example, the water-pump or thermostat is replaced), DME will continue to maintain Mapped mode (around 80 oC). DME will perform system performance tests and measurements. Only then, when all necessary parameters of components of the cooling system will be measured and DME will make sure, that they meet the norm, only then DME will turn on High power mode (with engine temperature 95 oC). After a certain time, DME will “dare” to perform in Normal mode (with temperature 105 oC), after a while – Eco mode (112 oC) will be turned on.

This check-up time takes quite a lot of time and even driving conditions – unfortunately, it’s not possible to speed up this process of self-diagnostics.


Notice: if the repair of the cooling system is done, it’s necessary to perform re-adaptation of the engine.


Simple way, how to check, if the thermostat performs as it is supposed to.

At first: cold/cool engine – disconnect the heating of the thermostat.

Then: start the engine, heat-up at idle. Till moment, when the temperature in the area of thermostat reaches 90 oC, the pipe, which drains the liquid to the radiator, should be cold! If the pipe gets warm even then when the engine is still heating (significantly below 90 oC), the thermostat is damaged and has to be replaced!


Finally, more exact about MSD80.

The engine temperature can be seen here:../F5/F2/F6

In the image: engine temperature marked with red color.


Power (PWM) of cooling fan: ../F6/F1/F1

Thermostat heating: ../F6/F1/F4

Management of water-pump: ../F6/F1/F8


In cold weather: if MSD80 heats the thermostat (value, visible in ../F6/F1/F4, is higher than 0), obviously, the engine temperature is maintained lower than High power mode (95 oC). In this situation, we have to pay attention to conditions, because of which the engine can work in Mapped mode (listed above).

If ../F6/F1/F4 indicates 0, the temperature of cooling liquid has to be close to 90 oC, the engine temperature: 95 oC. If temperatures correspond to numbers mentioned, thermostat works correctly. If temperatures for a longer time (driving evenly) stay lowered – thermostat is damaged (stuck in partly open position).


Note: the cooling system has high thermal capacity and inertia, evaluation of the temperature has to be done in a longer period of time (at least 10 .. 15 minutes).