I drive an '06 a4 cabriolet. Did some searching and think my heater core is a reason for some coolant loss as now it doesn't leak when I have the AC/Heater unit off as I drive, which is in town around a couple miles. I turned on my heater full blast and it blows cold air. Should I order a new heater core, and try to clean out the heater core and flush the coolant system for any air bubbles? Or wait on ordering the new part and clean out the core and coolant systems...

 

Update: I had my coolant bypass replaced, but then the coolant housing went bad, so I replaced that and a hose. Soon after, my check engine light came on with my engine shaking. Did some research before I took it to O'Rielley's for a diagnostics test (that's a couple miles away and they check for free). They said I had a misfire from cylinders 2 and 4, so I bought and replaced the spark plugs and ignition coils for both. Pretty easy DIY if you have the tools and you can learn by watching some youtube videos. I bought plugs and coils for the other two cylinders but have not put them in yet. Engine runs without shaking, but the engine light is still on. Took it to O'Rielley's very soon after and they said the engine needs to run a bit before the engine can pick up that I replaced the plugs and ignition coils. Next on my list is to find out what I need to change for my low oil pressure. I'll still keep updating my thread if more things pop up...

 

Anyway, after fixing the plugs and coils I had to have my water pump and timing belt replaced because they went out soon after. In two weeks it's been running great. Even took care of my low oil pressure warning.