I drive a 2002 Audi A4, 1.8T Quattro. The other day I requested my local Audi dealer to flush my coolant. I have been loosing coolant and I also believe I am running on the wrong type of coolant for more than a year now (mine shows a greenish type of coolant in the reservoir instead of the pink G12. What do you think?). The dealer told me they cannot flush my coolant until they replace the thermostat housing plug, it is leaking. They provided me with part# 06B-103-033-A. This will take them approx. 3.5h and will cost me around $400. I have no problem fixing this issue since it will hopefully solve my coolant problem. I looked up a picture of this thermostat housing plug, and found the one attached to this post. It’s next to the actual thermostat itself and that’s why I asked the dealer if it would be beneficial to also change out the thermostat itself while they’re down there. The dealer told me not to worry about it at this time. I am driving my car in severe winter weather mainly in town. Sometimes it does not even fully warm up. Summers here are mild.

I wonder about your opinion. Would you insist they change out the thermostat at the same time; I have around 72k on this vehicle and would assume the thermostat will fail at some point? What do you know about this thermostat housing plug? Is this a common item that fails?

Thanks!