When should I replace my auxiliary belt?

By Adam White

The auxiliary belt is an often-overlooked but extremely important component of any car. It drives a range of components, such as the alternator, water pump, power steering pump, and air-conditioning compressor and is connected to these components via the crankshaft pulley. In some cases (albeit rare), it also drives the cooling fan. Sometimes it is known as the 'Serpentine' belt because of the way it twists around multiple pulleys in a river-like fashion.

Tyre replacement

As we have already mentioned, the purpose of the auxiliary belt is to 'drive' or 'power' several important components.

The first of these components is the air conditioning compressor. This removes vapour refrigerant from the air conditioning system's evaporator. There are three main types of air conditioning compressor: the two-cylinder reciprocating Piston type, the four-cylinder radial type, and the six-cylinder Excel type.

The second key component is the power steering pump (PAS). This is the central component of the steering systems found in most modern cars. The PAS creates the hydraulic pressure that makes your steering wheel easier to turn. It receives its power from the engine via the auxiliary belt.

Another key component, the water pump, is usually driven by the auxiliary belt from the sprocket or crankshaft pulley. The water pump keeps coolant running through the engine, cylinder head, radiator, and hoses and helps maintain an optimum temperature.

The alternator is another vital component that is driven by this belt. The alternator works in tandem with the battery and provides the power for the main electrical components, such as the interior/exterior lights and the dashboard/instrument panel. The alternator is usually found near the front of the engine, mounted using brackets. Alternators produce AC (alternative current) power using electromagnetism.

What does the auxiliary belt look like?

The auxiliary belt is usually long, wide, and flat - and is often 'toothed' - meaning that it has teeth moulded into its surface. Toothed belts have low/zero slippage and do not need lubrication. They are usually made from high-quality reinforced rubber and are designed to last several years and to provide reliable power to all of the important components outlined above.

Signs that your auxiliary belt may need repairing/replacing

There are a number of indications/signs that your belt may need replacing. The main ones are:

- Loss of power steering or increased difficulty in steering

- No cool air blowing out from the vents of the air-conditioning system

- Engine appears to be overheating

- The battery warning light is on - this could be because the belt is not powering the alternator and the battery is running down

- Squealing sounds from the front of the car

- A whining noise from the engine

Sometimes the belt may simply need tightening a little, whilst on other occasions, it may need replacing. A broken auxiliary belt will not cause catastrophic damage to the engine but will require immediate replacement.

How to diagnose auxiliary belt problems

If you are experiencing some of the above issues and are able to physically inspect the auxiliary belt, you should look out for the following:

- Significant cracking or obvious signs of wear in the spine/ribs of the belt

- A shiny and/or frayed appearance

- A hardened surface with a clear lack of flexibility

- Signs of contamination, for example, from oil or coolant.

If you see any of the above signs of damage when you inspect your belt, it is likely that you will need to replace your auxiliary belt as soon as possible.

How long should an auxiliary belt last?

This can vary significantly depending on various factors, most notably the use of the vehicle. Having said that, as a rule-of-thumb, they should last between 50,000 and 100,000 miles or around five years. Replacement belts are inexpensive and usually only take a few minutes to change.

How can you make your auxiliary belt last longer?

Regularly checking the belt for damage and checking/adjusting the tension levels can help to extend the life of the belt, as can ensuring that it is clean and free of contaminants.

How to replace auxiliary belts

Whilst it is technically possible to replace the belt yourself, in our experience, it is always advisable to have this done professionally by qualified mechanics who will have done it hundreds of times. At Protyle, we can replace the auxiliary belt for you when it breaks/wears out.

How much will it cost to replace?

The cost of the replacement will depend on the age, model, and make of the car.

Protyre - the tyre experts and more!

In addition to offering services such as auxiliary belt replacement, Protyre garages offer MOTs, servicing (we check the condition of the belt as part of the Gold and Silver service packages), free safety checks, and tyre fitting.

All Protyre garages offer a wide variety of tyres. This includes high-quality products from premium brands such as Pirelli, Goodyear and Michelin; low-cost/economy options from brands including Budget, Ovation, Autogrip, Enduro-Runway; and mid-range options from the manufacturers such as Sumitomo, Hankook, Falken, and GT Radial. Tyres available include summer tyres, winter tyres, all-season tyres, 4x4 tyres, extra load (XL) tyres, and run-flat tyres.

Booking your car in for a service, MOT, or tyre fitting with Protyre is quick and easy. You can book online or over the phone. To find your nearest Protyre garage, simply enter your postcode in the online search function - results will be displayed in a list with the nearest garage shown first and the locations can also be viewed on a map).

Find My Protyre

Share with your friends...

About the author

Article Author Photo
By Adam White
Adam looks to create engaging and informative content across the website that provides consumers with expert advice on MOTs, servicing, vehicle maintenance and tyre care. As a motorsport enthusiast, Adam enjoys documenting the Protyre Motorsport team’s involvement in major motorsport events across the UK.
View authorArrow right
AGM and EFB Battery Fitments Explained
If you have a Start-Stop engine, you need a Start-Stop battery. These batteries have been developed specifically for Start-Stop engines and can quickly recover power lost as a result of starting the engine. On many modern cars, the battery isn’t where you think it might be; other than in the engine bay, the battery can be found in the boot, under the passenger seat or under flooring. It can take up to two hours to change the battery on some vehicles! Even if the battery is in the traditional area, it can take a long time to fit a replacement battery; the battery box may be under another part or tucked behind a difficult to remove piece of equipment.
Find out moreChevron
How to fix a dead car battery?
A dead car battery is one of every driver's worst nightmares, but it's a problem most of us have had to endure at least once.
Find out moreChevron
What happens if you put the wrong battery in your car?
The importance of fitting the right battery in your car is often overlooked. It's true that many batteries are interchangeable across the same class of car, but there are some crucial considerations to bear in mind.
Find out moreChevron