If you remove the thermostat, you will need to block the hose between the head and the waterpump. The stock thermostat closes the bypass as it opens for the main flow. The thermostat is on the suction side of the pump. Any type of restriction on the suction side of the pump will increase the chances of cavitation. Spinning the pump faster than designed will also cause cavitation. Using a radiator from an 85 golf that came with factory AC is a cheap upgrade. Another mistake I see people make is with the fitting on the back of the cylinder head and the resevoir tank. We run the coolant tme sender in the hose fitting. The resevoir should be plumbed into the middle fitting on the waterpump. This insures all coolant flow is out the head into the top of the radiator. Plumbed this way, it should be self bleeding. Ducting between the radiator and the front grill as the factory did does help. If you find the engine runs too cool, you could fabricate a restrictor to fit under the coolant flange on head. We have not found that we need one in the Southeast.