Coolant Bleeding

Coolant Bleeding

The E46 cooling system is notoriously difficult to bleed. Trapped air causes overheating and inaccurate temperature readings.

Bleed Procedure

1. Fill expansion tank to MAX with coolant mixture
2. Open bleed screw on thermostat housing (7mm)
3. Fill until coolant flows from bleed screw without bubbles
4. Close bleed screw
5. Start engine with heater on full hot, fan on low
6. Monitor temperature gauge
7. When thermostat opens (~97°C), coolant level will drop
8. Top off expansion tank as needed
9. Repeat until level stabilizes
10. Drive and recheck level when fully cool

Tips

• Raise front of car slightly (ramps) to help air escape
• Squeeze upper hose to help move air bubbles
• May take 2-3 heat cycles to fully bleed
• If temperature spikes briefly then drops, air is still present