Hey all
After my 00 A6 4.2l sat for a year, we had the transmission replaced and the rear o2 sensor wires spliced back together (rodent damage). Now it is over heating and most of my mechanic budget is gone. Can anyone point me in the right direction for diagnosing this? The big fan that is crank driven spins all the time, the other 2 only when the climate control is running. It is getting hot both in traffic and on the highway. The coolant is also disappearing but I am not sure where it is going. When hot you can see the reservoir empty rapidly but barely drips underneath car. Lots of steam. Also there was CEL for coolant temp sensor circuit, turned out the sensor was never plugged into coolant reservoir. Cel gone, still overheating.

Thanks in advance!
Kristen