Coolant Temperature Sensor -Engine Coolant Sensor

What is the engine coolant temperature sensor? How does it works?

Why do we need to install it in our coolant system?

Let me start with an introduction to the human body, whenever we have a fever temperature of the body goes up in that case extra heat need of body need to be dissipated. This is important because temperature variation of 4℃ to 5℃ more than normal temperature for a certain period could cause many problems to our nervous system or other parts of the body. That is why we went to less hot surroundings or use wet clothes to dissipate heat faster. Here is the normal temperature range of the human body 36.5-37.5℃ or 97.7-99.5℉. And how do we know our body temperature by using a measuring device call thermometer?

What is Engine coolant?

SI or CI engine (spark ignition or compression ignition ) generally works on Otto- Diesel cycle.
A mixture of Air+Fuel (chemical energy ) ignite inside the cylinder and create high temperature-pressure gases which drive or push the piston to convert this energy into useful work. In this whole process about 30% of energy converted into work and the rest of the 70% need to dissipate from the engine to the surrounding area. To transfer such amount of heat from the engine never an easy process. The small engine of bike or motorcycle with a displacement of 100 to 250cc maintains the required temperature by dissipating extra heat to surrounding by natural convection or forced convection.
But for an engine having a displacement of 350cc or more need a liquid-cooled cooling system which is more effective and rate of heat transfer should be  faster than bike or smaller engine.

"Coolant" is a mixture of clean water added with Antifreeze, this water-based coolant circulates around the engine head and absorbs heat further absorbed heat transfer to a unit called radiator where hot coolant cools down by releasing heat to the surrounding. 

Coolant Temperature Sensor 

We all know that driving  a vehicle to get the maximum or optimum level of efficiency and performance through it engine need to be at specific temperature means excess heat of engine (use less energy or heat ) needs to be release with a level of effectiveness. So to measure how cold & hot coolant is ' A temperature measuring device all thermostat installed in Cooling lines or inside radiator unit'. 
Based on operational requirements different types of Temperature sensors available to measure coolant temperatures like Thermistor, Thermostat, or Thermocouple.

Example Heat  Release Cycle

Coolant temperature sensor connected with an ECU (Engine Control Unit) through the wiring harness. 
ECU sends electrical current to sensor-based on the temperature of coolant resistance of sensor varies this results in a change in the output of the sensor.ECU converts an electrical signal into a processable data and compares it to reference data stored in memory during testing of the engine. Based on temperature range ECU make the decision to adjust fuel injection, ignition, timing. 

This temperature also is shown on the dashboard of the car so that drivers can have a better idea of what's going with the engine.

How to check faulty Coolant Temperature Sensor?

A faulty or bad temperature sensor can cause a range of engine-related problems like engine overheating, poor performance, poor acceleration, and leakage. Not so common but some time faulty sensors result in an expensive part replacement. To avoid and identify faulty or bad temperature sensor check following things
  • Start ignition switch and check for Engine check light 
  • Start Engine takes a reading of coolant from a dashboard in a case without driving dashboard shows temperature more than normal temperature 45℃ or 113 ℉. Same time use an external temperature sensor to measure the coolant temperature in the radiator and compare it with the dashboard reading variation should not be more than 5℃ to 8℃.
  • Check blockage into cooling lines or pipes
  • Check wiring Harness & connection 
  • Check for external & internal crack or damage 
  • If possible run the diagnostic program and reboot ECU
  • Check Again if any change 
  • Replace Temperature sensor or contact to a service center  

Effect of Faulty Coolant Temperature Sensor

  1. Poor Fuel Economy 
  2. Slow Acceleration 
  3. Engine Heating 
  4. Low performance 
  5. Damage of cooling lines 
  6. Engine overheating might cause damage to expensive parts

Replacement of Temperature Sensor 

    1. Location of Sensor

Generally Coolant temperature sensor (CTS) located near radiator or thermostat housing. Some vehicles located near the bay of the engine and need a proper light source to find it.

   2.Removal of Connector and Cables

Before removing the temperature sensor physically remove wiring or cable connected to it. Cable connected through a female or male connector just pressing connector plug it easily came out form housing of temperature sensor. If needed replace the cable with a new one beside connector.

   3.Removal of Faulty Sensor

Some time due to dirt and water oxides sensor thread jam with radiator unit, so squirt a release spray on housing this will easy the unscrewing process. Temperature sensor threaded like nut and blot using a recommend size socket and apply small torque. Be gentle because some time thread gets stuck with the unit or broke inside it.

 4. Installation of Temperature Sensor

Before installation of new sensor remove dirt, corrosion if any on threaded area. Apply a lock-tight to ensure leakage free connection. Use a socket to apply recommended torque gently and slowly.

 5. Test or Check 

After installation of a new sensor check its reading by switching to ignition mode or on engine start. To check whether it works properly start the engine and accelerate it to a higher RPM for 5 min and check variation in temperature if it is satisfactory STOP the engine. Check for Engine check light if everything seems OK you good to go with this sensor.

Safety Pre-Caution during sensor replacement Process

  1. Ensure Coolant & surrounding Engine area has to be at normal temperature 
  2. Use heat resistance gloves
  3. Use Manuals provided by OEMs
  4. Use proper socket
  5.  Have Extinguisher near your work area


Coolant temperature sensor have very important role in engine life, performance. This small pieces of sensor save more money of a owner by indication level of temperature of coolant to take proper action before got into serious issue.Sensor is cheap around $30 to $50 and replacement can be done by inexperience  person but need supervision from expert.
owner need to follow OEMs time schedule of service for Vehicle to avoid problem.

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