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Your Coolant Temperature Sensor (Coolant Sensor) worn out? » Read more about common malfunctions • Repair • Replacement manual
To prevent the engine from overheating: the engine coolant temperature sensor (ECT sensor)
The coolant temperature sensor is a smal but important component. It guards the engine and can initiate a protective mode. A defect is usually detected and signalled by the control unit.
Engine coolant temperature: function
The engine coolant temperature sensor monitors the coolant temperature. The coolant flows through the engine, removing excess heat. When the coolant becomes too hot, the engine can sustain damage. In most cases the cylinder head gasket burns out. If driving is continued despite escaping hot steam a piston seizure is imminent which would damage the engine beyond repair. In order for protective functions to take effect, sensors for the coolant temperature are installed.
At least three sensors in the car
A car always has three sensors installed. They have the following tasks:
- engaging the radiator fan
- indicating the coolant temperature on the dashboard
- alerting the control unit.
When the engine temperature approaches the maximum safety limit, the radiator fan switches on, actively conducting fresh, cool air through the radiator and lowering the coolant temperature. If this is not sufficient, the control unit switches the car in emergency mode or in the worst case switches it off completely. The third sensor permanently transmits the actual temperature showing on the dashboard. In case of overheating, it is marked by a "red zone" or the check light switches on.
ECT sensor: construction
The engine coolant temperature sensor consists of a thin bimetal strip, connected to two contacts. The strip and the contacts are enveloped in a water-tight housing. When the temperature changes, the bimetal strip bends and changes the electric resistance. This is registered by the control unit or the other actors (indicator or radiator fan) and sets them in operation.
ECT sensor defects
The sensor's weak point is its housing. Moisture penetrating the housing causes corrosion of the internal contact points and the bi-metal strip. These all consist of thin metal and rust eats away the inside of the sensor in a a few days, resulting in the sensor supplying erratic data. Most vehicles register this. In older cars this can become a problem as interpretation requires some professional expertise. A defective sensor shows the following symptoms:
- the engine temperature indicator is always on "cold"
- the fan does not engage or runs permanently
- a cold engine starts very reluctantly
- increased fuel consumption.
The car is constructed in such a way that as a rule it does not sustain any direct damage from a defective sensor. Nevertheless it should always be replaced in order to bring the car in its normal condition. The temperature sensors of the car have specified replacement interval by the manufacturer. Following these instructions and regularly replacing all sensors will keep the car free from malfunctions in this area.
Coolant sensor replacement
Fortunately, the coolant sensor is one of the easiest sensors to replace in a car. The sensor for the fan can be found directly on the radiator. It is a large messing bolt, screwed into the radiator. It is simply unscrewed and replaced by a new component. The sensors for the dashboard indicator and the control unit are usually placed right next to each other on a coolant hose or on the engine and fixed with a clamp. This is pulled out with needle pliers and the sensor removed. Prior to installing the new sensors, the contact points are cleaned.
Costs for an ECT sensor
The simple construction and its broad application range make the engine coolant sensor very cheap. Their price starts at ca. 10 EUR (± £9) and hardly ever gets higher than that. This makes replacing a defective sensor a cheap and quick repair. At these low prices, preventive replacement of the ECT sensors is not a problem either. This keeps you on the safe side, knowing these components to be fresh and new. This makes driving considerably more relaxed. Depending on the control unit, new sensors may have to be programmed in first. Information on this can be found in the operation and repair manual or the garage.