At what temperature does the BMW 320 thermostat open?
3 Answers
BMW 320's thermostat generally starts to open automatically when the temperature at the engine's coolant inlet reaches 103 degrees Celsius, without requiring DME control. Working principle of the thermostat: The commonly used thermostat is a wax-type thermostat. When the coolant temperature is below the specified value, the refined paraffin in the thermostat's temperature-sensing body remains solid, and the thermostat valve closes the passage between the engine and the radiator under the action of the spring. The coolant returns to the engine via the water pump, performing a small circulation within the engine. When the coolant temperature reaches the specified value, the paraffin begins to melt and gradually turns into a liquid, increasing in volume and compressing the rubber tube, causing it to contract. As the rubber tube contracts, it exerts an upward thrust on the push rod, which in turn exerts a downward counter-thrust on the valve, causing it to open. At this point, the coolant flows through the radiator and the thermostat valve, then returns to the engine via the water pump, performing a large circulation. Signs of a damaged thermostat: If coolant continues to flow out from the upper water chamber inlet pipe of the radiator when the engine starts cold, it indicates that the main valve of the thermostat cannot close. If there is no coolant flowing out from the upper water chamber inlet pipe of the radiator when the engine coolant temperature exceeds 70 degrees Celsius, it indicates that the main valve of the thermostat cannot open normally, and repair is needed at this time.
I've been running an auto repair shop for over a decade and have seen plenty of BMW 3 Series. The thermostat on a BMW 320 usually opens around 105°C, and this number is spot on! Both the N20 and B48 engines are set up this way. BMW does things differently - while regular cars open at around 80°C, BMW insists on waiting until 105°C, claiming it improves fuel efficiency by keeping the engine running hotter. But there's a catch with this design - during summer traffic jams, the temperature gauge can shoot into the red zone in no time. If you notice the temperature needle fluctuating or the heater not producing warm air, there's an 80% chance the thermostat is stuck. This component is connected to both the radiator and water pump, and DIY replacement often leads to coolant leaks, so I recommend taking it to a specialist workshop.
Last week, I just helped my brother replace the thermostat on his 2017 BMW 320. Actual testing shows that the car's electronic thermostat opens precisely at 105 degrees Celsius, with an error margin of no more than 3 degrees. BMW specifically switched from old mechanical thermostats to electronic ones for more precise control. However, electronic components are prone to issues. My brother's car once threw an engine fault code, which was diagnosed as low cooling system performance. To check for this, look for two signs: if the coolant temperature rises unusually slowly after a cold start, or if the temperature stays below 90 degrees during highway driving, it's likely the thermostat is stuck open. Replacing it with an OEM part costs over 2,000 yuan including labor, while aftermarket parts are around 800 but more likely to need repeat repairs.
