Battery light on and the temperature climbing?
Together, those two can mean the drive belt has come off, which stops the water pump and the alternator at once. Pull over somewhere safe and switch off. Don't push on with the gauge climbing or a red light showing, and never open a radiator or coolant cap on a hot engine. Call roadside assistance if you have it. If anyone is in danger, call 000.
When should an engine belt be replaced?
When the maker's schedule says, or sooner if it looks worn. Most modern engines run one ribbed belt around the outside, called a drive belt or serpentine belt. It turns the alternator, the air conditioning compressor, often the water pump, and the power steering pump on cars that have one.
This belt usually shows its age before it fails: cracks across the ribs, frayed edges, a glazed shine, or a squeal on a cold morning. If it's lost, everything it drives stops and the engine can overheat quickly.
Don't assume the belt is the whole story. A tensioner keeps it tight and idler pulleys guide it, and a tired bearing in either will chew through a new belt. One seized accessory can stall the whole drive too. A careful mechanic checks each pulley before fitting a new one. The hidden belt that runs the valves is a separate job: see cambelt replacement.
What do engine mounts do, and how do they fail?
Engine mounts hold the engine and gearbox in the car, on rubber or fluid-filled blocks that soak up vibration. Over time the rubber cracks and sags, or the fluid leaks out.
You'll feel it as a shake through the steering wheel or seat at idle, a clunk when you take off, or a thump going from reverse to drive. A worn mount lets the engine rock further than it should, which puts strain on hoses, belts and the exhaust. Most engines have several mounts and they don't all wear at the same rate, so ask which ones the mechanic found worn.
What the car's doing, and where a mechanic usually starts
| Usual place to start | Worth telling the mechanic | |
|---|---|---|
| Squeal on a cold start | The drive belt, tensioner or a pulley | Whether it stops as the engine warms up |
| Clunk on take-off | An engine or gearbox mount | Whether it happens in drive, reverse or both |
| Rough idle or shaking | Spark plugs, coils, injectors or an air leak | Whether the engine light came on |
| Ticking or knocking | The oil level first, then inside the engine | Whether it speeds up with the revs |
| Sudden loss of power | Fuel, air or the turbo, usually with a stored code | Whether the car dropped into limp mode |
How does a mechanic find the fault?
By asking first, then listening, then testing. A car scan shows any stored codes, but it points to an area and doesn't name the part. From there it's hands-on: watching the engine move, spinning pulleys, testing coils and checking for leaks.
If you've got a specific symptom, these pages go further: misfire or rough idle, knocking or ticking, limp mode and a squealing belt.
What if it's something bigger?
Sometimes the answer is inside the engine: a head gasket, worn bearings or low compression. Then the choice is repair, a rebuilt engine or a replacement. What decides it is the car's age and condition, how far the damage goes, and what the rest of the car is likely to need soon.
Don't let anyone rush you here. Consumer Affairs Victoria's advice is to ask for a written estimate before any work starts, and that matters most on a job this size. Under the Australian Consumer Law, repairs must be done with due care and skill, and that goes for any repair business.
What a good written estimate should show
- What was tested to reach the diagnosis, and what the test showed.
- Each part by name, and whether it's the maker's own, aftermarket or reconditioned.
- On a belt job, whether the tensioner and pulleys are included, and why or why not.
- On a mount job, which mounts are worn.
- Any machining that goes out to another business.
- Anything extra the mechanic found, listed apart so you can say yes or no.
What you can do, and what's the mechanic's job
You can
- Look at the belt with the engine off and cold. Take a photo of any cracks or fraying.
- Check the oil and coolant levels on a cold car.
- Record the noise on your phone and note when it happens.
- Write down any lights that came on, and any recent work.
Leave to the mechanic
- Fitting a belt: the routing and tension have to be right.
- Replacing mounts: the engine has to be supported safely while they're out.
- Anything that means the car going up in the air, or a hot engine with coolant in it.
What we'd do
We'd treat a new noise as information, not a verdict. Note when it happens, whether any light came on, and get it looked at before it turns into a tow. A squealing belt or a clunking mount shouldn't wait for the next service. If the word rebuild comes up, we'd ask to see the test results and get a second opinion before saying yes. Send it through and take the first step from there.