The coolant tank to the left rear of the engine compartment is where you fill the coolant. The tank behind the license plate is the overflow and once you fill the coolant system properly, this is where you can check and keep the level up to proper spec.
best thing to do is fill the bottle as best you can before starting the engine. You'll need to lift the front engine of the vehicle slightly so the radiator is higher than the engine. (in theory, it already is, but thats the way VW wants you to do it.) Also make sure all of the heater temp controls are moved to the hot position.
Remove the upper radiator grill and at the top left side (as you look at it) of the radiator you'll see a small screw. Loosen it up, you don't have to remove it.
Start the engine and let it idle, adding coolant to keep the tank as full as possible. I usually boost the idle a little so the engine warms faster and the coolant flows quicker. After a little while, as the engine warms, you should first hear air coming out of that little screw in the radiator and then as the air is bled out, you should see coolant. When the air is out, tighten the screw. Fill the rear tank and replace the cap.
What I usually do here is, put the van back on the ground, fill up the tank behind the license plate and then take the van for a ride. Keep an eye on the temp gauge and blinking light. If the light comes on you may have to stop and put more coolant in. Becareful, because now everything is hot! Open the cap slowly. Sometimes, just loosening the radiator cap on the tank is enough to bleed out the little bit of air built up.
Once you've finished the drive around let the engine sit (up to a few hours) and check the coolant level in the two tanks. At this point, the main tank inside the engine back should have no air in it. If it does, just top off. Check the over flow and Top off the overflow to the proper level and you're good to go. Over the course of a few days any leftover air should bleed itself out. Just keep an eye on the overflow tank.
Good luck.
