I had to change a stuck open thermostat in my 2005 BHW B5.5 Passat which opened my coolant system. All coolant I drained from the radiator looked like it was in great condition. Everything went well and now my engine temperature doesn't drop on the highway. Since then, I have had the occasional gurgle in my dashboard, but seems more likely when under load. AC system is not on, so it is not refrigerant. Heat appears to work just fine. I have performed multiple incarnations of the purge process with the weeping hole on the hose. Engine on, engine off, coolant cap open, coolant cap closed, lifted reservoir, etc. I thought it would purge itself over time, but it doesn't seem to. I did not backflush the heater core or oil cooler. Is it possible air bubbles are getting trapped in the heater core? I can't imagine that my heat would work well at all if the core were blocked to the point of holding back air. I would like to prevent the gurgling, but isn't worth a ton more time investment. Is there any issue with air in the system? I recall reading corrosion or wear issues. Any pointers on the next steps?