What tells the radiator fan to kick on?
The radiator fan in a vehicle is triggered to turn on when the engine coolant temperature reaches a certain threshold, typically around 200-220°F (93-104°C). This helps regulate the engine temperature and prevent overheating by drawing air through the radiator and dissipating heat.
How the Radiator Fan Works
The radiator fan is an essential component of a vehicle's cooling system. It is responsible for drawing air through the radiator, which helps to dissipate the heat generated by the engine. The fan is typically controlled by a temperature sensor that monitors the coolant temperature. When the coolant temperature reaches a certain threshold, the sensor signals the fan to turn on, ensuring that the engine does not overheat.
Factors that Trigger the Radiator Fan
There are several factors that can trigger the radiator fan to turn on, including:
- Coolant Temperature: The primary trigger for the radiator fan is the coolant temperature. When the coolant reaches a certain temperature, typically around 200-220°F (93-104°C), the fan will turn on to help cool the engine.
- Engine Load: The engine load can also affect when the radiator fan turns on. Under heavy load, such as when towing a trailer or climbing a steep hill, the engine generates more heat, which can trigger the fan to turn on sooner.
- Ambient Temperature: The outside air temperature can also play a role in when the radiator fan turns on. In hot weather, the fan may need to run more frequently to keep the engine cool.li>
- Fan Control Module: Many modern vehicles use a fan control module to monitor various sensors and determine when the radiator fan should be activated. This module can override the temperature sensor and turn the fan on based on other factors.li>
By understanding the factors that trigger the radiator fan, you can better diagnose and troubleshoot any issues with your vehicle's cooling system.
What triggers the radiator fan to turn on?
The radiator fan turns on when the engine's coolant gets too hot, usually triggered by the engine's control unit (ECU) or a thermoswitch in the radiator when the coolant reaches a set temperature (around 200−230∘F200 minus 230 raised to the composed with power cap F200−230∘𝐹 or 93−110∘C93 minus 110 raised to the composed with power cap C93−110∘𝐶). The fan may also activate when the air conditioning is on or when the car is idling in traffic, as these conditions generate more heat that needs to be dissipated.
This video demonstrates how to check your radiator fan's relay: 46sCB7 MediaYouTube · Jul 10, 2022
Primary triggers
- High coolant temperature: The primary trigger is when the engine coolant temperature exceeds a preset limit.
- Coolant temperature sensor: A sensor measures the coolant's temperature and sends this data to the engine's computer.
- ECU or thermoswitch: The ECU, or a dedicated thermoswitch in older systems, receives the signal and activates the fan to pull air through the radiator and cool the coolant.
- Air conditioning use: The fan is often activated when the air conditioning is turned on to help cool the condenser, which is part of the A/C system.
- Idling or slow driving: The fan runs more frequently when the car is stopped or moving slowly because there is less natural airflow over the radiator to cool it.
This video explains how to diagnose a radiator fan that won't turn on: 59sMechanic BaseYouTube · Oct 9, 2023
What sensor tells the radiator fan to turn on?
The engine coolant temperature (ECT) sensor turns on the radiator fan by sending a signal to the car's computer (ECU) when the coolant gets too hot. The ECU then activates the fan to cool the engine. In older or simpler systems, a dedicated thermo-switch in the engine or radiator may directly control the fan relay without a computer.
This video shows how a coolant fan switch works and how to bypass it: 57sCarsNToysYouTube · Jan 28, 2022
How it works
- Modern vehicles (ECU-controlled):
- The ECT sensor measures the coolant's temperature.
- When the temperature exceeds a preset threshold, the sensor sends a signal to the Engine Control Unit (ECU) or Powertrain Control Module (PCM).
- The ECU receives other inputs, such as when the A/C is turned on, and then decides to turn on the radiator fan by activating its relay.
- Older vehicles (thermo-switch controlled):
- A thermal switch, often located on the engine block or radiator, has a specific temperature rating.
- When the coolant reaches that temperature, the switch completes an electrical circuit.
- This completes the circuit for the fan's relay, which then turns the fan on. The fan turns off again when the temperature drops below the switch's lower threshold.
You can watch this video to learn how to wire a radiator fan switch: 1mWiring RescueYouTube · Jan 30, 2022
Will the radiator fan work if the temperature sensor is not working?
If the coolant temp sensor is not reporting the engine is hot, the computer will think the engine is cool and not kick on the fans. If the sensor is unplugged, the computer will kick on the fans since it has a fault mode or safety built-in.
How do radiator fans know when to turn on?
Modern cars tend to have electrical fans that are powered by the vehicle's electrical system. This allows them to be more efficient (they are sensitive to temperature and only operate when extra cooling is needed).
