My 2010 XF was parked for 15 minutes & when I returned, there was a puddle under the car. I drive it 3 blocks home & it was smoking. Had it towed to mechanic next day who added coolant & did a pressure test. No leaks etc. After leaving it sitting overnight, all coolant disappeared. No signs of leaks etc. Ideas?

Airlocks in the cooling system? Can cause excess pressure in the expansion/header tank and force coolant out leaving even more air in the system. Top up each morning when cold and try to park overnight with the front of the car nose down if the expansion tank is by the bulkhead like in the S Type or if the expansion tank is near the front, face uphill to help get the air out.