How Do I Stop My Fan Belt from Squeaking?

Nothing kills your style behind the wheel more than a horrible sound that can be heard by passing pedestrians and motorists alike. From squeaky brakes to wheels rubbing on the wheel arch, whether you drive a backdated Porsche 911, a Cal-Look Beetle or a more practical daily driver, like a Golf or a VW T5 the piercing squeal of a fan belt is a noise no one wants to hear. 

You have come to the right place though. Let us explain what causes this to happen, and what you can do to fix a squeaky fan belt.

A fan belt, also known as a drive belt, is a crucial component that keeps various engine systems functioning. It helps drive essential components like the alternator, water pump, power steering and cooling fan. Over time, and especially during the damper and colder seasons, your fan belt may begin to emit a high-pitched squeal, which can happen for the following reasons.

1. Wear and Tear: Classic cars are known for longevity, but rubber belts degrade over time. Cracks, glazing, or fraying can cause the belt to slip, leading to squeaks.
2. Improper Tension: A belt that is too tight or too loose can result in noise. Overly tight belts can prematurely wear the bearings of the component in question, whilst loose belts slip and squeak as they struggle to gain grip. 
3. Dirt and Debris: Dirt, oil, or other contaminants on the belt can cause slippage and squeaking.
4. Misaligned Pulleys: If the pulleys are misaligned, the belt won’t move as smoothly, or grip as well, leading to that tell-tale squeak and increased belt wear.
5. Temperature and Humidity: Sudden changes in temperature and moisture levels can temporarily affect the belt’s tension, or grip levels and cause squeaking. 

A fan belt is not to be confused with a cambelt or timing belt. We explain more about how a timing belt works here. 

There are several reasons your vehicle could be making mysterious noises, but here is how to go about diagnosing the issue as the fan belt. 

Before lifting the bonnet or engine lid, ensure all loose clothing and hair are tied well out of the way. 

• Listen Carefully: Start the engine and listen to identify where the noise originates. A fan belt squeal is typically high-pitched and more likely to occur under acceleration. Generally, it will come from the front or an easily accessible part of the engine. 
• Observe Engine Behaviour: If the squeak stops once the engine warms up, the issue may be related to temporary expansion due to temperature. Equally, you may find that it only occurs if it has been raining, or when you have driven through a large puddle. Get someone to rev the engine whilst you watch and listen. 

With the engine switched off. 

• Visually Inspect the Belt: Check for signs of wear, like cracks or fraying. Also, twist the belt, push it in and pull it out, to test for incorrect tension. 
• Check the Pulleys: Examine the condition of the pulleys and tensioners. Surface rust or heavy wear marks will indicate the need to renew this component. 

There should be approximately 1/2" or 13mm deflection when pressing in the centre of the belt. Likewise, if you twist the belt between your thumb and finger it should turn about 90 degrees.

Too tight, and the belt will put pressure on the bearings within the components it is attached to. Too loose, and you will have issues with slippage, unwanted noises and inefficiencies in the charging system. Does your car battery keep going flat? Check out our blog here.

Numerous drive belts are available depending on the application, so it's not a simple one-size-fits-all, I'm afraid. 

The good news is your old belt will have the sizes and specifications printed on it, to help you source a replacement. There are a few factors to look out for.

• The belt length: This will be the largest number on the belt, measured in millimetres (in most cases).
• The belt width: The measurement at the widest point, in millimetres. This may also use the designation letter A (1/2" or approx 13mm) or B (5/8" or approx 16mm). 
• Smooth or cogged belt: Both do the same job, however, the cogged design offers better grip and the ability to flex when navigating smaller pulleys. The cogged design also helps to dissipate heat when in use. A cogged belt will carry the designation letter X in its identification code. 

If you are referencing a fan belt on a parts website, you may find there are multiple versions listed for your vehicle. It might be that a longer belt is required for a vehicle with Power Steering or Air Conditioning fitted, so double-check both the specification on your car, and the measurement on your old belt to be sure you get the right one. 

There are products available from Motor Factors, and online marketplaces that claim to fix the issue of noisy fan belts with a simple spray from an aerosol. 

We've not used these personally, preferring to get to the root cause, and solve the issue for good, but here is what we know.

• Belt dressing is applied either by spray or as a wax to the inside surface of the fan belt. 
• Belt dressing works by softening the rubber of the fan belt, increasing its friction properties, and helping to eliminate slip.
• It's important not to spray this fluid onto components nearby. You certainly don't want to increase the friction in your alternator or water pump bearings!
• Using a belt dressing to soften it can increase the wear on the belt, especially when applied to already perished or dried-out rubber. 
• When it comes to fitting a replacement, you should clean off the belt dressing from all pulleys and tensioners to avoid contaminating the new belt. 

The good news is a replacement drive belt for your car is not an expensive purchase. In fact, we would advise you to carry a spare, especially if you drive an aircooled vehicle which relies so heavily on the fan belt to ensure the engine remains at the correct temperature. Find out all about aircooled engine cooling here. 

Removal of a fan belt is fairly simple and follows the same theory regardless of the vehicle. You need to remove the tension, to allow you to loop the belt off the pulley. This can be done by:

• Splitting the front and back half of the pulley from each other, allows the belt to be slipped off and replaced. This is done on aircooled VWs such as the Beetle or the T2 Bay. 
• Loosening of a component that is mounted on a pivot, which acts as a belt tensioner. In the case of a watercooled VW, this is usually the alternator.

Refitting, as they say, is the same but in reverse. In the case of a two-part alternator pulley, you will need to use shims in between each half to adjust the belt tension. More shims between the two pulley halves will loosen the belt. Removing the shims will tighten it. Surplus shims should be stored behind the pulley nut.

With an alternator (or similar) acting as a tensioner, this can be moved closer or further away from the engine pulley, and fastened tight to get the correct belt tension. 

We hope this article has helped answer a few of your questions, and hopefully steered you in the right direction for fixing your squeaky alternator or power steering belt. 

Got any questions, fire away. Got any additional tips we should add? Pop them in the comments section below. 

Andy