What a lovely morning, you don’t think, as you blow into your gloves on another chilly December morning.
It’s dark. You can hear the quiet rush of the early A38 traffic.
That’s normal. Until you turn your key in the ignition and, suddenly, a deathly screech fills the air.
It lasts only a second. Sometimes a couple. But then, it settles down again, and you go about your day, wincing and raising an apologetic hand as your neighbours glance over at you.
We’ve all been there. Don’t worry. The good news is, there’s something we can do about it. Here at Sunset VW, we see Volkswagens, Audis, Seats and Skodas with problems like this all the time. This page explains the most likely causes and how to fix them.
Auxiliary drive belt slip
The auxiliary drive belt, sometimes called the serpentine belt, is the rubber belt you can usually see on the outside of the engine when you open your bonnet.
Also known as the drive belt, it’s connected to a pulley on the crankshaft, the bit of the engine that spins round. When this turns, the belt makes lots of other pulleys spin.
These pulleys power things like the alternator (which recharges the battery and runs electrical systems), the air conditioning compressor or the hydraulic power steering pump and water pump. There’s also a tensioner in the system, which presses against the belt to keep it tight.
That screeching sound when you start your VW is most likely the drive belt slipping. In other words, it isn’t quite tight enough. Especially at start-up, and even more so in the damp and the cold, that sudden load might make the crankshaft pulley slip past the rubber belt a couple of times before it grips.
The drive belt could also be glazed or cracked, caked in dirt or dust or grease, or misaligned on the pulleys.
It shouldn’t take long before the belt grips, though, and the screeching sound fades away once your engine’s revs settle down.
There are a couple of common hacks to stop this noise, but we advise against them. Get the root cause fixed, often by simply installing a new belt, so it doesn’t develop into something worse, like a snapped belt or seized pulley.
If you have the technical know-how and the tools, you can replace the belt at home. However, if you’re at all unsure, give Sunset VW a call, and we’ll be happy to take a look.
Belt tensioner or idler pulley wear
As we mentioned, the belt itself is, in most cases, the problem. Replacing it should fix that screeching sound when you start your VW.
However, if it doesn’t make any difference, the next things to look at are the belt tensioner and the idler pulleys.
Tensioners press into the belt to keep it tight as the engine speed changes. Idler pulleys guide the belt along its route, so it doesn’t slip off the important pulleys. The bearings inside these parts will eventually wear down, causing the belt to slip or lose consistent tension.
Whether the tensioner isn’t tightening the belt, or the idler pulley isn’t spinning properly, you’ll get that screech or chirp when you start your VW. It may also return later, especially at idle or low engine speeds.
Diagnosing and replacing these components requires a bit more technical know-how, so book an appointment with Sunset VW and have us take a look for you.
Alternator pulley or alternator bearing issues
The alternator is a critical part of your VW. The drive belt turns the alternator pulley, which spins a metal piece inside the alternator.
Thanks to a few clever laws of physics, this generates a current that recharges your battery and powers the lights, heating, ECU, etc as you drive.
However, if the pulley fails (or starts to fail), the shock load from starting your engine puts it under extra strain. And that will likely result in a screeching sound.
Many VWs use an alternator pulley with a built-in one-way clutch that lets the alternator spin independently of the engine when the engine speed changes. When this pulley fails, the alternator no longer decouples from the belt properly, causing belt vibration and screeching noises at start-up, even though the belt may still be in good condition.
One key sign that the alternator pulley is the problem is that the noise returns at other times, particularly when you put the car under additional electrical load. That means when you do things like turning on heated seats or playing the radio extra loud. You might also see a battery warning light.
A failing alternator or alternator pulley is a serious problem. The best way to check your alternator is to bring your car to us. Our friendly team will take a look and run a charging test to identify the root cause.
Air conditioning compressor drag
Another pulley driven by the drive belt powers the air conditioning compressor. The compressor forces the refrigerant through the system, which exchanges heat back into the atmosphere, leading to that pleasant cooling sensation that can be so refreshing in summer.
If your car doesn’t have air conditioning, you won’t have an air conditioning pulley, so this won’t be causing that screech when you start your VW. There may be an idler pulley there instead.
Like all the pulleys in the system, the air conditioning pulley always spins, even if you have the AC switched off, as most of us probably do at this time of year. There’s a little clutch to connect the pulley to the compressor, and that’s what engages when you turn on the air conditioning by pressing the button.
Extra resistance in this pulley could cause that squealing sound. You can narrow down the problem by checking whether the noise changes when the air conditioning is on or off.
This fault is unlikely to pose an immediate danger to your car, though the air conditioning might not work as well or at all. However, get it repaired as soon as possible, as continued pressure increases strain on the drive belt and risks compressor failure.
Other pulleys
The other pulleys powered by your VW’s drive belt vary from car to car. For example, as we touched on above, not every car has air conditioning, so those models don’t have an A/C pulley.
In the same vein, most modern cars use electric power steering, powered by an electric motor. The drive belt doesn’t power this, and therefore, it requires no pulley. However, hydraulic power steering, found on most vehicles up to around 2010 or 2011, uses a drive-belt-powered pump, so these do have a pulley.
Some older VWs may also have belt-driven water pumps to circulate coolant through the engine. However, most cars now have water pumps attached to either the timing belt or powered by an electric motor. Still, it’s worth checking if you have one.
These pulleys, or their bearings, can wear or start to drag, which may cause a screeching sound when you start your VW. A technician will replace them, and that should stop the noise.
Starter motor and flywheel engagement noise
Up until now, we’ve been looking at screeches that happen only once the engine starts. But if you hear that squealing sound while the engine’s cranking, then the problem isn’t anything to do with the belts or the pulleys.
When you turn the key, the starter motor engages. This has a tiny pinion gear that meshes with the flywheel, which is connected to the crankshaft. The starter motor turns the pinion gear which, in turn, spins the crankshaft and gives the engine the momentum it needs to start.
However, if that pinion gear gets damaged or doesn’t engage the flywheel properly, the gears scrape instead of meshing cleanly. This may well produce that sharp screeching sound you hear.
The tell here is that you’ll only hear that sound while you’re holding the key. As soon as the engine starts and you let go of your key, everything will sound normal.
Now, there are several possible causes, but you can remedy the vast majority with a new starter motor. In very rare cases, the flywheel gears themselves may be worn, requiring a much more complex repair. Avoid further flywheel damage by getting this problem fixed as soon as possible.
Quick self-check to narrow it down
You can do plenty of self-investigation work at home without any specialist tools or even knowledge about cars. If the screech:
- Is only during cranking → starter or flywheel.
- Starts after the engine fires → something in the belt drive system.
- Is worse on wet or cold mornings → belt slip.
- Changes when the A/C switches on → belt or A/C pulley.
- Returns with electrical load → alternator or alternator pulley.
The more information you can bring us, the better. It’s details like these that help us diagnose the fault faster, and get you back on the road sooner.
Here at Sunset VW’s service centre in Derby, our friendly team has made it our mission to help local residents keep their VWs, Audis, Seats and Skodas safe, efficient and comfortable. We’ve heard all manner of engine screeching sounds at startup over the years, and we’ll help you understand the problem and how to fix it.
So, if you have a screeching VW engine, even if you’re pretty sure it’s just the belt, book it in for a service or check-up. A short inspection now can help prevent a simple issue from becoming an expensive one later.