Why is there a loud fan noise in the car engine?

This blog post will answer the question, ‘Why is there a loud fan noise in the car engine?’, and cover topics like different faults in radiator fans and their diagnosis, how does a car engine fan work, and different car engine fan configurations.

Why is there a loud fan noise in the car engine?

These are the following reasons behind a loud noise coming from the car engine:

  • Fan blades getting dirty
  • A defective cooling system
  • A loose or worn-out radiator fan belt
  • Defective radiator
  • Hindered airflow in and around the radiator

Different faults in radiator fans and their diagnosis

These are the different faults in radiator fans and their respective diagnosis.


A fuse protects all electrical components and in case of a short circuit, it cuts off the electric current flowing towards these components to protect them from further damage. A blown fuse can either be caused by a problem in the wires of the radiator fan.

Faulty ECT

A faulty engine coolant temperature sensor (ECT), is a big cause behind a faulty radiator fan as it sends an erroneous signal to the electronic control unit(ECU), thus not being able to turn the cooling fan on when it is needed.

Damaged radiator fan wirings

In the case of an overheating car, the cause can be a faulty or corroded wiring system that connects the radiator fan to the engine. All wiring and cable networks should be checked along with the relay unit.

Broken fans

This is a pretty straightforward cause of a malfunctioning car engine fan as they are made up of electric motors. These motors either with frequent usage or with the passage of time become worn out and might malfunction if ignored for long.

Defective fan relay unit

The radiator fan of the engine draws a lot of power and needs a support system. The fan relay unit helps in powering up the cooling fan and in some cases can get damaged or corroded. This leads to the car engine fan not turning on.

Defective control module

There is a control module to monitor the usage of the engine cooling fan. Usually, the control module of the engine cooling fan is set up in the engine bay. This location exposes it to the heat from the sun and also the formation of dust, dirt, debris, and other forms of gunk.

How does a car engine fan work?

The car engine fan is a crucial part of the cooling system of the car. The car engine fan is generally fitted behind the radiator and is usually mounted on the water pump shaft. It induces a flow of air through the radiator block.

This function becomes essentially important when the vehicle is moving slowly, or when it is stationary and the engine is idling. The fan is generally driven by a V-belt from the engine crankshaft.

The car engine fan has a number of blades that are either made from metal, nylon, or some other plastic material. As the number of fan blades increases, the fan size can be reduced.

It is important to note the proper adjustment of the car engine fan belt. If the fan belt is too tight, the dynamo and the water pump bearing may be damaged and excess absorption of power might occur. 

If the fan belt is too slack, the efficiency of the cooling system and the dynamo output will be affected.

Another important point to be noted is that the engine crankshaft should not be rotated by the fan blades as this will result in the distortion of the fan blades and the fan assembly will run out of balance.

Different car engine fan configurations

These are the following types of car engine fans and their characteristics.

Metal fans

These types of fans possess a simple design and are easily set up. However, they are heavy and can increase the weight of the engine and thus cause a lack of engine efficiency

Fully molded fans

These types of fans are beneficial for ensuring maximum airflow and they help keep noise levels to a minimum. The downside of these fully molded fans lies in the fact that they are not as flexible as the metal fans.

Modular fans

These types of fans offer a number of customizations that can be done and ensure maximum possible airflow along with minimal noise. They also increase engine efficiency. The only downside lies in the fact that these types of fans are expensive and also have a complex setup.

Research shows the different engine cooling fan requirements and the types of airflows of a car engine fan.


This blog post addressed the question, ‘Why is there a loud fan noise in the car engine?’

We understood the various faults that can occur in car engine radiator fans along with their diagnosis and how a car engine fan actually works. Furthermore, the different configurations of a car engine fan have also been discussed. Please feel free to comment on the content or ask any questions in the comments section below.

Frequently Asked Questions (FAQs): Why is there a loud fan noise in the car engine?

What does an engine fan do?

An engine fan helps to regulate the engine temperature by keeping it cool when needed, according to the requirements.

How much does it cost to replace an engine fan?

A replacement of the engine fan usually costs 530-670$.

What happens if your radiator fan stops working?

If the radiator fan stops working, the engine might undergo overheating and can seize if not fixed with immediate effect.