Editorial Feature

How Coolant Temperature Sensors Regulate Antifreeze for Effective Engine Cooling

Ever wondered how your car keeps its engine from overheating, no matter the weather? That’s where the Engine Coolant Temperature Sensor (ECTS) comes in.

Close up of a car engine

Image Credit: ARVD73/Shutterstock.com

This little device plays a big role in making sure your engine stays at the right temperature by monitoring the coolant—also known as antifreeze. It sends data to the engine control unit (ECU), which then adjusts various engine functions to maintain optimal performance.

This article will break down the fundamentals of coolant temperature sensors, explaining how they work, why they matter, and what happens when they fail, answering key questions such as:

  • What is an ECTS?
  • What are the main components of an ECTS, and how does it work?
  • What happens when a coolant sensor fails, and how can faults be detected?
  • Who are the leading manufacturers of ECTS technology?

What is an Engine Coolant Temperature Sensor?

An ECTS is one of those behind-the-scenes components that keeps your car running smoothly. It is responsible for monitoring the temperature of the coolant-antifreeze mixture and relaying data to the ECU. Since engines generate a significant amount of heat, maintaining the right operating temperature is essential to prevent overheating and ensure efficiency. The ECU uses the information from the ECTS to make real-time adjustments that regulate engine performance.

This small sensor has a huge impact on the overall performance of your engine. It helps regulate fuel injection timing, making sure the right amount of fuel is delivered based on the engine's temperature. It also plays a role in ignition timing, determining when the spark plugs fire for optimal performance and fuel efficiency. And when things start heating up, the ECTS signals the ECU to kick on the radiator fan, keeping the engine cool and preventing overheating.

Antifreeze does more than just stop coolant from freezing in winter—it also keeps it from boiling over in hot weather. The ECTS keeps an eye on these temperature changes, allowing the ECU to make adjustments before things get out of hand. If the coolant gets too hot, the ECU can tweak various engine settings to cool things down and prevent damage.

You’ll typically find the ECTS in or near the thermostat housing, where it gets an accurate reading of the coolant’s temperature. Because it’s in such a strategic spot, it can quickly send feedback to the ECU, ensuring precise control over the engine’s cooling system. In short, the ECTS is a small but essential part of keeping your engine healthy, making sure it runs efficiently and stays at the right temperature no matter the conditions.

What Are the Main Components of an ECTS?

The ECTS may be small, but it’s built with several key components that allow it to function accurately and reliably.

At its core is the NTC thermistor, a ceramic semiconductor that changes resistance based on temperature. It typically has a resistance of 2.5-3.0 kΩ at 20 °C, with a beta value of 3300-3500 K, which determines how its resistance shifts as temperatures change. This relationship follows a predictable pattern where resistance decreases as temperature rises, and it is described mathematically by the Steinhart-Hart equation:

1/T=A+B(lnR)+C(lnR)3

where T is the temperature in Kelvin, R is resistance in ohms, and A, B, and C are specific to the thermistor’s material properties.

To ensure accurate temperature readings and long-term durability, the conductive metal housing—typically made of brass or stainless steel—protects the sensor from coolant exposure and extreme temperatures ranging from -40 °C to +130 °C.

The hexagonal corona, a 19 mm or 3/4" hex fitting, allows for precise installation, with a typical torque specification of 15-20 Nm to prevent leaks. Meanwhile, the thread, often an M12 or M14 with a 1.5 mm or 1.25 mm pitch, ensures a secure, pressure-tight seal in cooling systems that operate at 15-20 PSI.

The electrical terminal is a two-pin connector, usually made from a copper alloy with gold or tin plating to resist corrosion and maintain conductivity. As vehicles operate in demanding conditions, this terminal is designed to withstand vibrations from 10-500 Hz and temperatures up to 125 °C.

Inside the sensor, Kovar wires serve as the conductor, carefully selected for their thermal expansion properties that match glass, ensuring a hermetically sealed electrical connection. These wires typically range from 22 to 26 AWG for stable signal transmission.

The ECTS operates by generating a voltage signal based on temperature changes. The ECU supplies a reference voltage—usually 5 V—to the sensor. Inside the ECU, a voltage divider circuit pairs the ECTS with a fixed resistor. As the thermistor’s resistance changes, the voltage output shifts accordingly. This signal, typically ranging between 0.5 V and 4.5 V, is processed through the Analog-to-Digital Converter (ADC) in the ECU, which translates it into an accurate temperature reading.

With this real-time data, the ECU can make necessary engine adjustments. If the temperature changes, the ECU may modify fuel injection timing by ±5 %, advance or retard ignition timing by up to 10°, or activate the radiator fan when the coolant reaches 93-96 °C. Additionally, the ECTS helps determine when to switch the engine into closed-loop feedback control, which typically happens around 70 °C, allowing for more precise fuel and emissions management.

By continuously monitoring coolant temperature, the ECTS helps prevent overheating, optimizes engine efficiency, and protects vital components from heat-related damage. Its precise measurements and rapid response—typically under five seconds for a 63.2 % temperature step change—ensure that the engine maintains a stable temperature under varying operating conditions.

What Happens When a Coolant Sensor Fails, and How Can Faults Be Detected?

A faulty ECTS is one of the most common reasons for engine overheating. While most vehicles have dashboard alerts for high temperatures, they don’t always warn drivers when the sensor itself is malfunctioning. If the ECTS fails, the ECU might receive incorrect temperature readings, causing the engine to run too hot or too cold. This can lead to performance issues, reduced fuel efficiency, and, in some cases, serious engine damage.

A Case Sudy

To better understand these failures, a 2019 study looked into ECTS anomalies using telemetry data from a single vehicle in two different conditions—idling and driving. Researchers tested ten different one-class classifiers to see how well they could detect three levels of sensor malfunction. They developed an anomaly detection system with four main components: data acquisition, feature extraction, feature selection, and classification.

For real-world data collection, the team used an embedded system connected to the OBD-II interface of a 2014 Toyota Etios (1496 CC engine). A Carloop microcontroller-based development kit with cellular connectivity captured vehicle data at a rate of one sample per second (1 Hz). This setup allowed them to continuously monitor ECTS behavior and other engine parameters.

Instead of just flagging odd sensor readings, the system focused on contextual anomalies—analyzing sensor data in relation to overall vehicle performance. To do this, they used a sliding window approach for feature extraction, incorporating 27 different parameters, including the standard deviation of engine coolant temperature.

The researchers also examined seven additional vehicle parameters—engine load, RPM, long-term fuel trim, tank level, manifold absolute pressure, and catalyst temperature—to determine which factors were most relevant for detecting ECTS faults.

After analyzing the data, they found that RPM and coolant temperature were the most critical attributes, along with the standard deviation and variance of ECTS readings. To ensure accuracy, all attributes were normalized to a (0,1) scale before feeding them into the anomaly detection models.

For detecting anomalies, the researchers used one-class classification techniques. The system was trained on data from normal ECTS operation (with no active Diagnostic Trouble Codes) and then tested to see how well it could identify deviations. They evaluated various machine learning approaches, including support vector machines (SVM), rule-based systems, neural networks, statistical methods, and instance-based techniques.

The results showed that the one-class SVM with a third-degree polynomial kernel worked best for detecting anomalies while the vehicle was moving. However, when the engine was running but the car was stationary, the k-nearest neighbor (KNN) classifier performed better. These findings highlight how machine learning can help with early ECTS fault detection—potentially preventing overheating issues before they turn into serious problems.

Key Players in the ECTS Market

Several major companies are driving innovation in automotive sensor technology:

  • Robert Bosch GmbH: A global leader in automotive technology, Bosch continues to develop cutting-edge sensor solutions for vehicles.
  • Texas Instruments (TI): TI is advancing automotive safety and intelligence with semiconductor innovations like the AWR2544 77GHz millimeter-wave radar sensor, designed to enhance ADAS decision-making.
  • Honeywell: Known for its broad range of sensor technologies, Honeywell remains a key player in the automotive sensor market.
  • Sensata Technologies: This company is focused on advanced sensor solutions, including suspension pressure sensors for Active Suspension Systems in electric vehicles.
  • NXP Semiconductors: A major force in automotive sensors, NXP is investing heavily in R&D to push the boundaries of sensor technology.

These companies are constantly working to improve sensor efficiency, accuracy, and reliability. For instance, Sensata Technologies is developing solutions to help vehicles meet stricter emissions regulations while enhancing safety features. Meanwhile, Texas Instruments is refining sensor accuracy through semiconductor advancements, as seen in their latest automotive chips aimed at improving vehicle intelligence.

With growing concerns over road safety and the rise of connected vehicle technologies, the automotive sensors market is on track to reach USD 41.08 billion by 2030. This growth is being fueled by continuous innovation and strategic partnerships among these industry leaders.

The Bottom Line

So what is your key takeaway from this article? Your car’s ECTS is a crucial player in keeping your engine at the right temperature. By monitoring the coolant-antifreeze mixture and working with the ECU, it helps regulate fuel injection, ignition timing, and radiator function.

With ongoing research into anomaly detection and smarter sensors, drivers can look forward to even more reliable and efficient cooling systems in the future.

Want to Learn More?

Interested in other key vehicle sensors and how they impact performance? Check out these topics:

With advancements in automotive technology, sensors like the ECTS are becoming more sophisticated, ensuring better performance, efficiency, and safety. Stay informed about the latest trends and innovations to keep your vehicle running smoothly.

Keep this resource handy—download the full article now!

References and Further Reading

  1. Ahmed, I. (2020). Engine Coolant Temperature Sensor in Automotive Applications. https://www.researchgate.net/publication/344327217_Engine_Coolant_Temperature_Sensor_in_Automotive_Applications
  2. Diarah, R. S., Osueke, C., Adekunle, A., Adebayo, S., Aaron, A. B., & Joshua, O. O. (2023). Types of Temperature Sensors. Wireless Sensor Networks-Design, Applications and Challenges. DOI:10.5772/intechopen.110648, https://www.intechopen.com/chapters/86707
  3. Tutunea, D., Ilie, D., Racila, L., Otat, O., & Geonea, I. (2022). Evaluation of temperature sensors used in automotive applications type NTC and PTC. IOP Conference Series: Materials Science and Engineering, 1220, 1, 012035. DOI: 10.1088/1757-899X/1220/1/012035, https://iopscience.iop.org/article/10.1088/1757-899X/1220/1/012035/meta
  4. da Silva Neto, E. F., Feitosa, A. R., Cavalcanti, G. D., Silva-Filho, A. G. (2019). Detecting anomalies in the engine coolant sensor using one-class classifiers. 2019 IEEE 90th Vehicular Technology Conference (VTC2019-Fall), 1-5. DOI: 10.1109/VTCFall.2019.8891367,  https://ieeexplore.ieee.org/abstract/document/8891367

Disclaimer: The views expressed here are those of the author expressed in their private capacity and do not necessarily represent the views of AZoM.com Limited T/A AZoNetwork the owner and operator of this website. This disclaimer forms part of the Terms and conditions of use of this website.

Article Revisions

  • Jan 31 2025 - The content of this article has been updated to include the most up-to-date research findings and correct previous inaccuracies.
  • Jan 31 2025 - References section updated according to the body update, using new sources as reference.
  • Jan 31 2025 - Title changed from "Inside a Car – Coolant Temperature Sensors" to "How Coolant Temperature Sensors Regulate Antifreeze for Effective Engine Cooling"
Samudrapom Dam

Written by

Samudrapom Dam

Samudrapom Dam is a freelance scientific and business writer based in Kolkata, India. He has been writing articles related to business and scientific topics for more than one and a half years. He has extensive experience in writing about advanced technologies, information technology, machinery, metals and metal products, clean technologies, finance and banking, automotive, household products, and the aerospace industry. He is passionate about the latest developments in advanced technologies, the ways these developments can be implemented in a real-world situation, and how these developments can positively impact common people.

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