Just in case your 2.0 Liter-powered VW (not sure of other engine designs) develops unexplained overheating with no external coolant leaks, it is most likely a internally shattered PLASTIC (yes you read that correctly) impeller that has failed. Unfortunately, it is about a 4-hour shop job to replace the impeller, since it is driven by the timing belt. So most of the front part of the engine must be dismantled in order to get to the impeller! COST: about $600-$750 parts & labor. If you are mechanically knowledgeable, parts (impeller, timing belt, tension pulley, and thermostat) will cost you about $210. When buying a replacement impeller, be sure to specify an ALL METAL replacement!
By your parts from an independent (not Pep Boys or the like) auto parts store that can supply you with German-made parts. A Bosch, all metal impeller would be ideal. A Continental timing belt or equivalent is best. It is cost effective to replace all the parts mentioned above during the tear down.