Coolant loss
Topping up coolant regularly? Find where it’s going — external leaks first, then internal.
HIGH RISK
Common symptoms
- Coolant level dropping
- Puddles/smell after parking
- Heater output changes
- Overheating episodes
Cost expectations
DIY: £0–£80. Garage: £120–£450+.
Note: prices vary by car and region. Use this as a planning range.
Most likely causes (ranked)
- External leak — Hose, radiator, thermostat housing, water pump.
- Pressure cap fault — Lets coolant boil off/escape.
- Heater core leak — Sweet smell inside, damp carpets.
- Internal leak — Head gasket, EGR cooler (diesel).
- Airlock/bleeding issue — After servicing; looks like loss.
Quick checks (fast, low-cost)
- Pressure test cooling system to reveal leaks.
- Use UV dye kit to spot slow leaks.
- Check inside cabin for damp and sweet smell.
- Check oil for contamination (not always present).
- Monitor coolant level at same temp/condition each check.
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
- Find external leaks before assuming head gasket.
- If no external leak, do combustion gas test.
- Fix small leaks early to avoid overheating.
AutoSolveHub helps you narrow possibilities. Always confirm critical repairs with proper testing and safe procedures.