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BMW engine temperature

BMW engine coolant temperature сorrector


Everyone knows the problem of fairly modern BMWs, and I think not only BMWs. The problem is the boiling of the engine to 108 degrees Celsius at low loads (such as traffic jams, waiting in a parking lot, etc.). The cycle is simple – when temperature reaches 108C, ECU resets the temperature to 105 by turning on the fan (in winter it doesn’t even turn on sometimes) and the electric pump to higher speeds, and then again in a circle.

Of course, when you start driving actively, the coolant temperature drops harshly and the oil temperature drops next. Obviously, it is dangerous to accelerate on an overheated ICE. Therefore, engineers have made a safer engine cooling cycle at power mode. A high operating temperature of an ICE means high pressure in the coolant system, oil coking due to overheating, low pressure in the oil system due to overheating of the oil, and many more reasons. These reasons are described in many places and many people have encountered them. It is clear that there are no critical values, but why should we risk.

My coolant reservoir exploded when I was just in the parking lot. I was watching how the oil temperature arrow for 30 minutes rises from 105 to 110 degrees. I changed the lid of the reservoir 4 days before. I am sure that if the coolant temperature was 85 degrees, this would never have happened.

Cold thermostat

This is a dubious decision for N54 / N55 engines, since there is an electric pump and if the thermostat opens earlier than necessary, the system will not turn on and the liquid will flow sluggishly through the radiator with practically no cooling and, of course, without cooling the engine.

There is an effect from it. It reduces the temperature in traffic jams by an average of 5-10 degrees (I collected feedback from the people who installed it).

Additional radiator

They install it for hot countries. Information from unverified sources says that there is a slightly different firmware, and this firmware regulates the temperature modes of the engine in a different way during operation.

There are too many problems for me. Therefore, I have discarded this option.

BMW engine coolant temperature сorrector

This is what the manufacturer calls it 🙂

Outwardly, it’s just a weird thing. But at the same time, it’s well built! It’s very easy to install in the engine and this thing becomes invisible for a layman. It uses factory connectors everywhere, and the wires tucked into a black cable duct.

You install the device on the upper hose of the radiator. It connects in-between the native temperature sensor. One end to the ECU, the other end to the DME. This solution is very convenient. Simple and efficient.

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BMW engine coolant temperature corrector

On modern cars, the following cooperatively working devices achieve temperature control:

Controlled thermostat
Radiator cooling fan
Radiator shutters
Variable displacement pump

DME activates all of them when the coolant temperature approaches 108-110 degrees. Alltogether, and not each separately. In contrast to the classic cold thermostat: when it is open, the cooling fan is off, and there is no point in this (purely academic case, in practice, a cold thermostat on “hot” firmware is really useful).

If we talk about good cold firmware, then it must correctly manage all the listed components. In other words, chip makers must intervene in the operation of important operating modes of engine components. Therefore, I have great doubts about the existence of such a firmware.

Now about the BMW engine coolant temperature corrector. As I already wrote, all engine temperature control mechanisms are activated when the coolant reaches the upper temperature threshold. According to the algorithm specified by the manufacturer in the DME. The thermostat corrector only shifts this threshold down by 12-15 degrees and does not affect anything else or interfere with the operation of other devices.

The point is this: increasing the transmitted temperature from the sensor to the system within 15 degrees. What does it do? Cooling fan turns on; electric pump works more intensively (if you have such option). The temperature seen by the system is corrected (shift upwards by an average of 15 degrees). Now, through the hidden menu, the average temperature is 110 degrees, but in fact, it is 95.

When the temperature reaches 93-95 degrees (in my case), this device corrects sensor readings by 12-15 degrees. In the 7th test, you can see a surge in readings. Starting from a certain point, we see that the temperature is 12-15 degrees higher than it actually is. The entire cooling system starts to operate at a lower temperature and operates normally. More information can be found on the internet.

I think this option is excellent, and I see no arguments against it. This is a ready-made, tested product for good money. Surely, this can be implemented through an engine firmware update, but not all engines have it. For myself, I chose this method, it seems to me simpler and more practical, and the installation of the device takes 15 minutes. You can remove the device at any time by yourself.

I’ve been driving with the BMW engine coolant temperature corrector for about 2 months now. No problems at all. The oil temperature dropped and in urban conditions, it is about 100 degrees Celsius. I don’t see real readings of the coolant temperature, apparently, it dropped by the same 12-15 degrees.

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Checking the electric fan with ECU at Peugeot & Citroen (PSA) without connecting to the car.

In order to check the electric fan with an ECU without a car, you need:

  1. First you need to measure the resistance between Signal and + Ubat (K.30). It should be between 1.5 kOhm and 2.5 kOhm. If the resistance is less than 1.5 kOhm or more than 2.5 kOhm, then this indicates that the fan is defective, or its life is coming to an end, despite the fact that it can still work for some time. When measuring the resistance between Signal and + Ubat (K.30), nothing must be connected to the fan except a measuring device!
  2. Next, you need to apply a 12 V supply voltage from the battery or power supply to the +Ubat(K. 30) and GND (K. 31) contacts of the power connector, designed for a maximum current of at least 30 … 50 A (depending on the type of fan).
  3. If there is a relay on the harness, then to turn it on, connect the + Relay input to + Ubat (K.30). And for a 4-pin connector, connect the -Relay input to GND (K.31).
  4. For CITROEN C3, you also need to drop +12 V to the Ignition input.
  5. If +12 V is applied to the Signal input or nothing is connected (left in the air), then the fan should gradually spin up to maximum speed.
  6. If mass (GND) is applied to the Signal input, the fan should stop completely.
  7. To smoothly change the speed, a pulse PWM signal with a frequency of 100 Hz must be applied to the Signal input.
  8. In order to check the Diagnostics output, connect a 10 kOhm resistor between + Ubat (K.30) and Diagnostics, and also connect a voltmeter between GND (K.31) and Diagnostics.Then apply 12 V to the contacts of the power connector + Ubat (K.30) and GND (K.31) from a source designed for a current of 30 … 50 A. Connect Signal input to +12 V or nothing. After the fan starts to spin up, measure the voltage between GND (K.31) and Diagnostics, it can gradually increase from 0 V to 1 V at the maximum fan speed. If the measured voltage exceeds 1 V at the maximum speed of rotation this will cause an error related to the fan malfunction recorded in the engine ECU. This error may cause the fan to work incorrectly or not start at all. But with this error, the fan can be started forcibly (as described above) or using the diagnostic program on the car itself.

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BMW thermostat problem

Since 1996, BMW began to install a controlled thermostat with an opening temperature of 105c on gasoline cars (as an example: thermostat 11537586885 for engine BMW n62, n63, n73, n74, s55, s63; thermostat 11537509227 for engine BMW m52, m54, m56; thermostat 11531436386 for engine BMW m62). Since then, the so-called BMW thermostat problem has been haunting these cars, because of the high operating temperatures, the wear and rapid failure of all engine units have sharply increased, as well as of the automatic transmission and exhaust system catalyst. For this reason, performance cold thermostats 11537586885, 11537509227, 11531436386 for BMW with an opening temperature of 90C appeared.

There is a strictly defined operating temperature for the engine that provides optimal working conditions. As a rule, within 90C. At lower temperatures, the engine oil does not have sufficient fluidity, which means that its resistance increases when the pistons move. At higher temperatures
– engine overheating (as an example, the above-mentioned BMW engines. One of the most common is n62, where the thermostat 11537586885 was originally installed with an opening temperature of 105c, not 90c).

The cooling system is designed to maintain an optimal operating temperature: when starting the car, you need a quick warm-up, and then, in the process of driving, you need high-quality cooling.   The thermostat takes over the regulation of this process, which is installed at the “fork” between the large and small circle of the cooling system and controls the direction of the coolant flow.

Until the engine is warmed up, the thermostat closes the pipe to the radiator, directing the coolant to a small circle: from the motor jacket, through the thermostat, bypass channel and back to the engine. Antifreeze does not pass through the radiator and does not cool, allowing the motor to warm up faster.

When the engine warms up to operating temperature (usually 90s), the thermostat opens the valve leading to the radiator, and the antifreeze begins to cool itself and cool the engine. Depending on the temperature of the antifreeze, the thermostat can close the valve to the bypass channel completely (when the engine needs intensive cooling) or partially.

Thus, the thermostat in a completely autonomous mode regulates the amount of antifreeze entering the cooling radiator, to keep the engine temperature at a constant operating level. On modern cars, thermostats can be equipped with an additional temperature sensor and heater (such as BMW thermostats 11537586885, 11537509227, 11531436386), paired with an electronic control unit. At medium engine speeds, the coolant temperature is maintained at a higher level (BMW thermostat problem), and at maximum load, additional heating is turned on, and the thermostat is triggered earlier, which allows you to reduce the temperature of the antifreeze by about 10°C. This decision can be controversial, since over time, the additional heater may fail.

Thermostat malfunctions: signs, causes, consequences.

Scale on the stem, corrosion on metal parts. As a rule, deposits in the cooling system appear due to poor-quality antifreeze and untimely replacement. Scale on the thermostat parts makes it difficult for the stem and valves to move, after that, the thermostat stops responding correctly to changes in the coolant temperature.

Failure due to vibration. More often, this problem happens with defective or low-quality products, in which the joints and connections are not sealed enough. If the copper cylinder is not sufficiently sealed, coolant will enter and prevent the thermostat from operating.

Destruction of the rubber seal due to high temperature. Overheating can disable the already “tired” rubber, after which it forms cracks and leaks. The membrane inside the working part (between the wax filler and the stem) also suffers from overheating.

If the thermostat breaks down, it begins to respond worse to temperature changes, and then it jams. The thermostat valves may block the pipe leading to the radiator or to the bypass channel, or they may stop in the middle position.

Malfunction signs:

The engine heats up for a long time – the pipe to the radiator is open, the antifreeze is cooled, preventing the engine from warming up.

The engine overheats (arrow is in the red zone) – antifreeze does not get to the radiator.

The engine heats up longer than usual, and under load the temperature rises sharply – the valves are stuck in the middle position, part of the coolant constantly passes through the radiator, but at intense driving this cooling is not enough.

Also, indirect signs of a thermostat failure may be non-working interior heating (the”stove” blows cold air, increased fuel consumption, deterioration of engine dynamics.

The worst consequence of a thermostat failure is engine overheating: in the heat, a few minutes are enough to bring the engine into emergency condition.  But driving with an insufficiently warmed engine affects its resource: wear of parts increases, engine oil works ineffectively.

How to check the thermostat?

  1. Start the engine. Before it warms up to operating temperature, antifreeze should not enter the radiator. Consequently, the pipe leading to the radiator must be cold. If it is warm – antifreeze enters the radiator ahead of time.
  2. When the engine warms up, the coolant should go to the radiator, the pipe should be warm.The engine is warmed up, but the antifreeze does not go to the radiator – the valve is closed.
  3. If the engine is well warmed up (almost to the red zone), the antifreeze should not enter the bypass pipe, but all pass through the cooling radiator. Accordingly, the pipe to the radiator will be hot, and the bypass pipe will be cold.

Another test method recommended by old-school car enthusiasts is to dismantle the thermostat and test it in hot water. Of course, if you wish, you can also evaluate the operation of the device, only you need to monitor the opening temperature of the valves. But if there are complaints about the operation of the thermostat, it is better to simply replace it. Thus timely installed performance cold thermostats 11537586885, 11537509227, 11531436386 for BMW engine n62, n63, n73, n74, s55, s63, m52, m54, m56, m64 with an opening temperature of 90C, will help to significantly save money in the future and solve the BMW thermostat problem.