If the problem started when the rad was replaced, I would let the car cool completely. Leave the motor off for hours or overnight. I would then, with the motor still off, double check the connections to the fans. Next, again while the motor is off, I would burp the system. You can do this by removing the rad cap over the turbo reservoir and gently squeezing the top rad hose. Keep at it, be very patient. Again, the motor is still off at this stage. After you've gone through that for a long, long while, then turn the motor on and let it warm up, burping it as it warms up. Be EXTREMELY CAREFUL now though because the motor is on, and the fans can come on at any moment! Make sure you get circulation when the thermostat opens, keep it topped off with coolant and burped, and see if that helps.