Volkswagen Repair: 2000 Jetta overheating, vw jetta, radiator fans

Question
I have a 2000 vw jetta gl 4cyl and it is overheating. We replaced the thermostat, temp. sender, thermoswitch (radiator)checked the water pump and timing belt and they are both working. The radiator fans switched on at about 225-250 F. We flushed the system and still nothing and are about at wits end and wary of taking it to a mechanic or heaven forbid the dealer. Do you have any ideas as to what might be wrong? It gets to temp (190 F) in about 5 minutes at idle and overheats after 15. We haven't dared take it out lately but before it would take around 8-10 minutes to overheat on 35-45 mph roads. Thanks in advance for your advice.

Answer
Two things.  First, you say you checked the water pump...How did you do that?  You also, changed the thermostat, and when you did, did you completely evacuate the cooling system down to 27 inches or so of mercury, and then wait for a few minutes to ensure the cooling system held vacuum, and therefore pressure?  If the cooling system was simply filled out of a gallon jug of coolant, there are still air pockets in Volkswagens that WON'T fill unless the vacuum refill method is use.  There is a special tool you can buy from MAC, or MATCO, or maybe a local specialty tool dealer that is called "AIRLIFT" and it is necessary to properly refill your VW.  As far as checking the coolant flow of the waterpump, you can do that by taking the small overflow hose off of the reservoir, and have someone in the car to run the rpm on the tach up to about 2200 rpm, and hold the hose over the open top of the reservoir.  If the flow stops, or gets really weak, your waterpump is done too.  Try that and see what happens.  Good luck, Robert.