Engine knocking
Metallic knocking/pinging under load can be serious. Rule out detonation vs mechanical noise.
HIGH RISK
Common symptoms
- Rattle/knock under acceleration
- Worse on hot days or low RPM load
- Possible loss of power
- May trigger misfire/knock control
Cost expectations
DIY: £0–£80. Garage: £150–£800+ depending on cause.
Note: prices vary by car and region. Use this as a planning range.
Most likely causes (ranked)
- Detonation (knock) — Low octane, too much boost/timing, lean mixture.
- Carbon buildup — Raises compression and causes hot spots.
- Low oil pressure — Bearing knock risk.
- Rod/main bearing wear — Deep knock that follows RPM.
- Accessory noise — Pulley/tensioner can mimic knock.
Quick checks (fast, low-cost)
- Try higher octane fuel and avoid low-RPM full-throttle.
- Scan for knock-related codes and check fuel trims.
- Check oil level/condition immediately.
- Use a stethoscope/long screwdriver to localise noise (carefully).
- If knock is deep and constant, stop driving and investigate.
Recommended tools
These tools make diagnosis faster and stop you buying random parts.
Related fixes
If your symptoms don’t match perfectly, check these next.
What to do next
- Detonation can destroy engines — treat as urgent.
- If oil pressure is suspected, do not keep driving.
- If it’s only under load, focus on fuel/air and tune factors.
AutoSolveHub helps you narrow possibilities. Always confirm critical repairs with proper testing and safe procedures.