BMW E46 Cooling System Bleeding
How do you bleed the E46 cooling system?
1. Fix the leak first, if there is one. 2. Start with a cold engine and open the bleed screw. 3. Add coolant to the expansion tank slowly until only liquid comes out of the screw, then close the screw. 4. Start the engine, turn the heater to full and warm up the engine. 5. Check the coolant level when cold. Raising the front of the car helps with bleeding, but on the M54B30 it is not necessary.
Can you open the cap or the bleed screw when hot?
No. Do not open the expansion tank cap or the bleed screw when warm or while the engine is running, because the coolant can boil and splash. The coolant level is checked and coolant is added only to a cold engine.
The heater does not get warm even after bleeding, what to do?
Air may have remained in the heater core, in which case the bleeding should be repeated with the front of the car raised steeply. If that does not help, the core may be clogged. It can be flushed or replaced with a new one.
The bleed screw leaks after being overtightened. What to do?
Replace the screw with a new one. The threads may still be stripped, in which case even a new screw may not stay tight. Thread locker has been tried, but there is no certainty that it works.