Why is the temperature gauge normal when the thermostat is broken?
2 Answers
Because the thermostat is designed to prevent the coolant temperature from dropping. Here are the relevant details: 1. How the thermostat works: The thermostat automatically adjusts the amount of coolant entering the radiator based on the coolant temperature, changing the circulation range to regulate the cooling system's capacity and ensure the engine operates within the appropriate temperature range. The thermostat must maintain good technical condition; otherwise, it will severely affect the engine's normal operation. 2. The role of the thermostat: To prevent the engine from becoming too cold. For example, after the engine reaches normal operating temperature, during winter driving, without a thermostat, the engine temperature might drop too low. In this case, the engine needs to temporarily stop the coolant circulation to ensure the temperature does not become excessively low. The most commonly used thermostat is the wax-type thermostat. When the coolant temperature is below the specified value, the refined paraffin inside the thermostat's temperature-sensing element remains solid, and the thermostat valve, under the spring's force, closes the passage between the engine and the radiator. The coolant returns to the engine via the water pump, creating a small circulation within the engine. When the coolant temperature reaches the specified value, the paraffin begins to melt, gradually turning into a liquid, expanding in volume, and compressing the rubber tube, causing it to contract. As the rubber tube contracts, it exerts an upward thrust on the pushrod, which in turn applies a downward counterforce to open the valve. At this point, the coolant flows through the radiator and thermostat valve, then returns to the engine via the water pump, completing a large circulation.
I just had my car repaired and found out why the thermostat was broken but the temperature gauge was working normally. It's quite simple. The temperature gauge relies on a sensor to measure the engine temperature and directly displays the reading, while the thermostat is just a valve that regulates coolant flow. If the thermostat is stuck open, the engine may run too cold, but if the temperature sensor isn't faulty, it can still display the correct low-temperature reading. If it's stuck closed, it may cause overheating, and only then might the temperature gauge show abnormal readings. Many people mistakenly believe that a faulty thermostat must affect the gauge, but they are actually two independent components. A normal temperature gauge doesn't mean everything is fine—running too cold can lead to insufficient engine lubrication, increased wear, and higher fuel consumption. It's recommended to check for unusual engine noises and perform regular maintenance to avoid issues.
