Our V6 runs fine but we changed the coolant approx 2000m ago and the front heaters only get warm ever since. I have tried running the engine with the bleed tube un-bunged and elevated but all that happens is after 20 minutes or so warm coolant begins to pour out of the tube. It isn't under pressure particularly and I can stop it with my finger on the tube but I was rather hoping for an ejection of air, not water.
I guess I'm going wrong somewhere but can anyone advise me?

Thanks
Dave