How an Automotive Engine Coolant Sensor Works: A Detailed Guide

Introduction

An automotive engine coolant temperature sensor, also described as a cylinder head temperature sensor, is designed to give feedback data to the engine computer about how hot the engine is running. This information is then used to make fine adjustments to the operating system designed into the computer which will affect engine performance and economy.

Adjustments are then made to the fuel injector pulse width, which is responsible for controlling the engine's fuel mixture and ignition system. Together these adjustments are a final result of the engine's power output and fuel economy capabilities and adjustments. This guide explores how the ECT sensor works and its components.

Coolant Sensor Duties

• Provide data to the engine computer
• Provide data to the temperature gauge (via engine computer)
• Illuminate the "engine hot" warning
• Turn on and off radiator cooling fans

How It Works

The ECT sensor is a thermistor-based device that changes resistance in response to temperature fluctuations inside the engine. The sensor uses a Negative Temperature Coefficient (NTC) thermistor, meaning its resistance decreases as the temperature increases. Coolant temp senders have two wires, one wire is fed 5 volts voltage from the computer, while the second wire is read by the computer and the engine temperature is determined. A coolant sensor wiring connector is held in place using a safety clip, there is also a weather pack seal that is designed to keep moister from the sensors electrical connectors which will cause corrosion which will alter the sensor's readings.

Malfunction

If the sensor is malfunctioning the gauge reading will be too cold, too hot or the warning light will be illuminated constantly. If the sensor housing is cracked it will allow moisture into the electrical connections, when this happens the coolant sensor should be replaced.

False Readings

When there is a coolant leak, or the engine has a blown head gasket, the coolant temperature sensor can be fooled because of the air or exhaust gasses trapped in the cooling system which the sensor cannot read. This is why certain conditions can exist that will be puzzling to the car's driver, for example; it is obvious the engine is overheating due to the steam being produced from under the hood, but the temperature gauge is read cold with no temperature warning light on. This is because the sensor element is not in coolant, therefore it cannot read temperature. For more information please visit - Symptoms of a bad Coolant Sensor

Locations

The coolant sensor's location is designed to monitor the engines coolant temperature where the coolant is the hottest, which is usually at the upper coolant hose outlet, (thermostat housing) or in the cylinder head near the combustion chambers.

How It's Made

The coolant temperature sensor is comprised of a metal housing filled with a composite which varies the resistance through its internal circuit as the engine temperature increases or decreases.

Older Cars

A coolant temperature "switch" was used in older cars to turn the engine temperature warning light on. A simple one wire temperature sender was also used to give feedback information to the temperature gauge in the dash.

Credits

This guide knowledge base was created by the 2CarPros Team, and by Ken Lavacot: Automobile repair shop owner and certified master automobile technician of over 30 years. If you have question or need help please ask one of our experts we are happy to help. Please visit our 2CarPros YouTube Channel.