Overheating, but cools down quickly? on 2004 Volkswagen Passat

My car started overheating (all the way into the red on the temperature gauge). Its got coolant in the resevoir, so it not that its short on coolant. After a few minutes of driving, then the temp starts climbing, but then it goes back down for a bit, then raises up into the red. What makes this really strange is it seems to cool down VERY fast. Like I can drive it again in 15 minutes as if it wasn't overheated. Any thoughts on what this could be? Thanks

by in Albany, CA on February 21, 2009
4 answers 4 comments
ANSWER by on February 22, 2009
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.
ANSWER by on February 22, 2009
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...........
ANSWER by on April 27, 2009
I just had to replace my water pump because it was doing just that same thing.
ANSWER by on February 14, 2010
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?
COMMENT by on August 19, 2010
Its the waterpump, although the ect sensors are garbage on the 1.8T's, It sounds like it s what that one dude said, its slipping due to the pump being stripped. almost every vw and audi ive seen in for a timing belt has had a crazy messed up waterpump... PRRR
COMMENT by on January 04, 2015
I too am having an over heating issue with my 2003. It has a new radiator, water pump, and thermostat. We even replaced the head gasket and torqued the bolts down in the proper order and spec. The new water pump is the second one we have tried and its aluminum. Any ideas what else could be wrong?
COMMENT by on April 01, 2015
A simple cause could be a faulty coolant cap try any parts store.
COMMENT by on July 27, 2015
Ok I have a 04 passat I just replaced the water pump&thermostat. I also put on new intake hose because it had a hole . The oil isn't mixing wit the water/coolant..ao I dont suspect the heads are cracked.. So I'm clueless about why its still overheating -plz help