Q&A

The water pump impeller on this engine is made from plastic and frequently the impeller part of the water pump fails. I'm not sure if the "new" VW supplied water pump still uses a plastic impeller but I would suggest using a good quality after market water pump with a metal impeller. It is funny that other European car manufacturers (BMW and Jaguar) have had the exact same failure when using plastic water pump impellers.
The water pump circulates coolant around the engine, you probably notice the engine presently overheats in traffic or under load but may cool when driving under light engine load on the freeway. On the freeway air rushing through the radiator will cool the engine.
Replacing the water pump is a pretty major repair taking approximately five and a half hours to six hours to replace.The timing belt must be removed. It is advisable if indeed it is a water pump failure that is causing your problem to replace the timing belt ,camshaft and crankshaft oil seals, flush the cooling system, and replace the cooling system thermostat at this time as these components are all easily accessible during water pump replacement. It would be a false savings if you keep the car and had to replace any of these other items a year from now.

Are the cooling fans running when the temp gauge is in the red ? If they are it is hot.
The reason I ask is the temp gauge display could be wrong , the sensor for this is a problem area. The gauge reading versus engine temp can be confirmed via scan tool or other means.
An overheated engine takes a lot longer than 15 minutes to cool down.
However coolant pump and thermostat failures are very common , especially if the coolant pump is the original...........

I just had to replace my water pump because it was doing just that same thing.

Interesting. On my 2004 Passat 1.8T, Thermostat replaced and cooling system flushed, heater works good. Cooling fans is a good clue I didn't think of, but how do you determine the sensor is bad? I was ready to replace the head gasket, suspecting a break between the water jacket and firing chamber. Also, check engine light diagnostics says intermittent misfire on #1 cylinder, which also made me think head gasket. Have you had any of these symptoms?