i know it's an old thread, but I found this DIY on blauparts.com and it seemed very thorough.......
How To Change Engine Coolant On A Vw 4 Cylinder (1998 - On) :
1. When the engine has cooled down, remove the Vw coolant tank cap.
2. Draining the Vw coolant from the 4cyl cooling system:
Remove the lower radiator drain plug from the lower front of the radiator (Vw A4, Vw Passat). Remove the passenger side lower radiator hose. Remove the outer Vw coolant hose that connects to the oil cooler. To drain the heater core you'll need to remove the hose on the coolant flange or transfer pipe located on the back side of the engine. This hose goes from the cylinder head to the heater core.
3. After the system is done draining, put the Vw coolant tank cap back on. Carefully work off and remove the smallest hose that is connected to the top of the Vw coolant tank. Be careful, the tank nipple likes to crack and break off.
4. With a blow gun and compressed air on low, carefully insert the blow nozzle into the small hose. Wearing safety goggles, carefully force the air out so that any Vw coolant that's still trapped in the cooling system is released.
5. Reinstall the Vw coolant drain plug. Reinstall the coolant tank hose(s). Fill the Vw cooling system with distilled water. Start the car and air bleed the cooling system as outlined in the factory Bentley manual. Run the car until the cooling fan comes on.
6. Repeat steps 1 through 5 until the water comes out clean.
7. Verify that you have the correct anti-phospate anti-amine G11 or G12 Vw coolant. If it's full concentrate, mix a 50/50 ratio per the Bentley manual. Fill your Vw cooling system with this 50/50 mixture. Note: Some factory Vw coolants sold by dealers are already premixed and do not require further delusion.
8.Run the 4cyl engine and check for any Vw coolant leaks.
9. Top off the coolant tank to the fill line. Do not overfill.
10. Using a permanent marker, write 'G11 or G12 Coolant Only' on the Vw coolant tank.
11. (optional) Be environmentally responsible and dispose of your old Vw coolant properly.
Vw Coolant System Maintenance:
1. Never top off the coolant tank with full concentrate G11 or G12 Vw coolant. Your Vw coolant should never exceed a coolant ratio of 80%. If it's over 80% an inefficient Vw cooling system will result, decreasing flow through the radiator along with poor heat transfer through the engine block.
2.Always top off your Vw coolant tank using a 50/50 mixture. If you're in a pinch and don't have any, use a small amount of distilled water. Remember, adding large amounts of water will change the alkalinity of the Vw coolant and throw off the glycol to water ratio, making it less effective in cold temperatures.
3. Never mix G11 blue coolant and G12 red coolant. It will turn into a brownish goo and plug up your Vw cooling system.
4. We highly recommend flushing your Vw's coolant when replacing your timing belt.
found it here..http://www.blauparts.com/vw/vw_fluid/vw_coolant_engine_fluid.shtml#vw4clycoolantchange