What is basically used for the coolant temperature sensor in modern cars?
3 Answers
Modern car coolant temperature sensors basically use a positive temperature coefficient thermistor. The relevant introduction to the positive temperature coefficient thermistor is as follows: Introduction to the positive temperature coefficient thermistor: It generally refers to semiconductor materials or components with a large positive temperature coefficient. The commonly mentioned PTC refers to the positive temperature coefficient thermistor, abbreviated as PTC thermistor. The PTC thermistor is a typical semiconductor resistor with temperature sensitivity. When the temperature exceeds a certain level (Curie temperature), its resistance value increases stepwise with the rise in temperature. Working principle of the positive temperature coefficient thermistor: The thermistor will remain inactive for a long time; when the ambient temperature and current are in zone c, the heat dissipation power of the thermistor is close to the heating power, so it may or may not act. When the ambient temperature is the same, the action time of the thermistor decreases sharply with the increase of current; when the ambient temperature is relatively high, the thermistor has a shorter action time and smaller holding current and action current.
I see that Hyundai's coolant temperature sensors nowadays mostly use negative temperature coefficient thermistors, which we call NTC resistors. This component is installed in the water jacket of the engine block or cylinder head, directly immersed in the antifreeze. When the temperature rises, its resistance value decreases instead, allowing the ECU to determine how hot the coolant actually is. Without this little gadget, the engine wouldn't be able to judge how much fuel to inject or when to signal the cooling fan. This can lead to noticeable shaking during cold starts, and the engine might constantly warn about high coolant temperature when warmed up. Just recently, I encountered a car where the sensor's wiring aged from prolonged immersion in antifreeze, causing inaccurate resistance signals. This resulted in the engine throwing a fault code, which was only resolved after replacing the sensor. During regular maintenance, it's best to have a mechanic check the sensor connector's sealing—if water gets in, it's trouble.
Modern automotive coolant temperature sensors commonly use NTC thermistors, installed in the engine cooling water passage. I've observed many vehicle models, and the principle of this device is quite simple: when the temperature is low, the resistance is high, and when the temperature rises, the resistance decreases, allowing the engine control unit to monitor coolant temperature changes. Older mechanical sensors relied on the thermal expansion and contraction of copper strips, but these electronic types react faster and have smaller errors. I've noticed that when they fail, they can easily cause a chain of problems, such as disrupting fuel injection leading to a surge in fuel consumption, or the fan not activating when it should, causing engine overheating. When repairing, it's also important to prevent coolant leaks. Last time, while cleaning rust from the sensor connector, I almost forgot to use sealant, and coolant seeped in. I recommend not spraying water directly at that black connector in the engine bay during car washes, as it's prone to water ingress and short circuits.
