Deep knock, or a red oil light? Switch off
If the knock gets louder with the revs, the oil pressure light comes on or the engine loses power, pull over somewhere safe and turn it off. Running an engine with low oil pressure can wreck it quickly, so don't try to make it home. Stuck somewhere exposed? Hazards on, everyone clear of the traffic, and call roadside assistance if you have it. If anyone is hurt or in danger, call 000.
Which noise have you got?
| Sounds like | Usually means | How soon | |
|---|---|---|---|
| Knock | A heavy, rhythmic thud from low in the engine that rises with revs | Something serious, NRMA says, often wear or low oil | Today. Stop driving it until it's checked |
| Ping | A faint metallic rattle when you accelerate hard, often uphill | Fuel with too low an octane rating, or poor tuning | Soon. Use the right fuel and tell the mechanic |
| Tick or tap | A light, fast tapping from the top of the engine | Low oil, valve train wear or general engine wear | Check the oil today, see a mechanic this week |
| Start-up rattle | A brief rattle right after a cold start | Oil draining from the hydraulic lifters overnight, usually gone in a second or two | Mention it at your next service, sooner if it lasts |
Why is a deep knock so serious?
The spinning parts inside your engine ride on a thin film of pressurised oil. When the oil runs low or the bearings wear, metal starts to hit metal, and that's the thud you hear. RACV says poor or low oil can stretch timing chains too, which can lead to major engine failure.
A mechanic needs to find what's moving that shouldn't be, and the sooner they do, the more of the engine there is to save.
Why does it ping, and will better fuel help?
Pinging is fuel going off at the wrong moment. RACQ says you'll usually hear it under hard acceleration from low speed, and that uncontrolled burning can quickly destroy parts such as pistons, head gaskets and valves.
Australian servos usually sell 91, 95 and 98 octane. RACQ says most cars sold here since 1986 accept 91, but your owner's handbook or the fuel flap label has the final word. If your car calls for 95 and you've been filling it with 91, go back to the right fuel first. RACV says modern engines often have sensors that adjust timing to protect themselves, at a cost to performance and fuel economy, so a car can lose power before you ever hear a ping.
Already on the right fuel and it still pings? RAC says poor tuning is the other common cause in petrol engines, and a mechanic will check that next.
What makes an engine tick?
Start with the dipstick. NRMA says a tap or click under the bonnet can simply mean low oil, which is easy to check. On older engines it can point to the valve train, and NRMA says some worn engines run for a long time like that, especially if the noise fades as the engine warms.
Many modern engines tick a little at idle as normal, so compare it with how your car has always sounded. New, louder or faster than before is what you're listening for.
What to do when you hear it
Listen properly
Radio off, window down. Note whether it's there cold or hot, at idle or under load, and whether it speeds up with the revs.
Check the oil on level ground
Park, switch off and let the engine cool, then use the dipstick the way the owner's manual says. If it's low, add the grade the manual names. If it's very low, tell the mechanic, because something is using or losing it.
Record it
A short video from the driver's seat with the engine running lets the mechanic hear it before they see the car.
What will the mechanic check?
They'll use a mechanic's stethoscope to place the noise, check the oil level and condition, and measure oil pressure with a proper gauge instead of relying on the dash light. They may inspect the oil filter for metal and check the timing chain on engines that have one.
This suits a mechanic who does engine repairs, not just servicing, because the answer can range from an oil top-up to opening the engine. Ask what they measured and what the reading means for the engine.
What you can do, and what's the mechanic's job
You can
- Check the oil level with the engine off and cool.
- Use the fuel grade your owner's handbook names.
- Note how many kilometres since the last oil change.
Leave to the mechanic
- Finding where the noise is coming from.
- Testing oil pressure with a gauge.
- Checking the timing chain, lifters and bearings.
- Deciding if the engine needs to come apart.
Our take
Deep knock: we wouldn't drive it any further, and we'd ask a mobile mechanic to listen to it where it sits. Tick with the oil low: we'd top it up with the right oil and send the job this week. Light ping: we'd fill up with the grade in the handbook, see if it settles, and have it checked if it doesn't. Whatever you're hearing, catching it early leaves you more choices.