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Notso Rent a coolant pressure tester and take it up to 1.3bar, and start looking. Once the system is leak free, put the drivers side front up on a jack stand so the thermostat is at a higher point, run the car with the rad cap off and the tool Mav1178 suggested installed and filled with coolant, run it for about 20mins or until the lower rad hose is warm, turn on the heater full blast and let it run for another 30mins or longer. You should see bubbles, that's a good sign.