lambda

If I were you I would change the heater matrix for a new one. It might be a matter of time until it starts to leak, or it might not, it's just my opinion. And bleeding the cooling system isn't always helping. I had the same problem and changing the heater matrix eliminated the swooshing sound and fixed problem with loosing coolant. If the heater matrix is dirty, rusted or blocked in any other way, the pressure of coolant is rising and the fluid is thrown out by the hole on the bottom of expansion tank. I'm sorry for digging up that old post, just wanted to share my experience with you