Got an A6 1999 2.8 . Replaced timing belt ,water pump at 80000 . Car start to overheat at 120000 , spot some coolant on top of my block . Would like to know where the thermostat is located ? Thanks

 

Thermostat is behind a channeling plate on the passenger side front of the engine and should've been changed along with the timing by. Coolant on top of the block means a leak from something else. These t-stats are failsafes, meaning they stick open when they fail, so a bad t-stat shouldn't cause an overheat.