Overheating at idle
Overheats in traffic but cools at speed. Usually airflow (fans/radiator) or coolant flow issues.
HIGH RISK
Common symptoms
- Overheats in traffic
- Temp drops when driving faster
- Fans not running or very noisy
- AC may stop working
Cost expectations
DIY: £0–£120. Garage: £120–£450+.
Note: prices vary by car and region. Use this as a planning range.
Most likely causes (ranked)
- Cooling fan fault — Fan motor, relay, resistor, wiring.
- Radiator blockage — External debris or internal scaling.
- Airlock — Trapped air reduces flow.
- Water pump weak — Impeller issue or belt slip.
- Head gasket pressurising — Less common; usually other symptoms too.
Quick checks (fast, low-cost)
- Check fan operation when temp rises (safe distance).
- Check fuses/relays for cooling fans.
- Use IR thermometer to check radiator hot/cold spots.
- Bleed cooling system properly if recently serviced.
- Pressure test if coolant loss accompanies overheating.
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
- Fix fans/airflow first for idle-only overheating.
- If coolant loss exists, investigate leaks.
- Avoid long idling until fixed.
AutoSolveHub helps you narrow possibilities. Always confirm critical repairs with proper testing and safe procedures.