What happens with excess coolant after performing BMW electrical cooling system bleed?

Question

I replaced a leaking hose on my BMW X3 2008 and attempted to bleed the cooling system according to these instructions.

Do not open the coolant expansion tank cap during the venting procedure.

1. Connect battery charger.
2. Switch on ignition.
3. Set heater to maximum temperature and turn fan down to lowest speed.
4. Press accelerator pedal for 10 seconds to floor. Engine must not be started.
5. The venting procedure is started when the accelerator pedal is pressed and takes approx. 12 minutes.(Electric coolant pump was activated and shuts down automatically after approx. 12 minutes).
6. Then top up fill level in coolant expansion tank with 100 ml above max (see illustration).
7. Check cooling system for leaks.
8. If venting has to be carried out again (e.g. if cooling system is leaking), allow DME to fall completely (leave ignition key removed for approx. 3 minutes), then repeat from Point 3.

After the bleeding procedure coolant level in expansion tank had dropped from "overfilled to neck" back to "normal". However, there was a new puddle of coolant below the car. This coolant did not leak out from bleeder screw hole or expansion tank cap that were closed all the time.

Is it normal for excess coolant during electrical bleeding procedure to get out from some other hole that I am simply not aware off? I expected that I will have to manually remove the excess coolant with turkey blaster. Or is there possibly another leak in the cooling system that I must troubleshoot?

Answer 1

The only way this would happen without being a problem is if the radiator cap or expansion tank cap were opened - older cars would be 'burped' in this manner, with the cooling system open, allowing air bubbles to leave via the cap and coolant to take its place, and the bubbles could cause splashes. Your BMW procedure specifically says not to. The cooling system is intentionally closed, hence the expansion tank for pressure relief.

Ergo, for fluid to escape, you've got another leak. Good luck finding it.

Of course, the final option is that the person filling the tank in preparation for the bleed accidentally spilt some :)