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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.

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