Q: After a radiator change, My car is shaking and emitting black smoke. What could be the cause? 2000 Volvo S80

Hello, your symptoms suggest a coolant temperature sensor failure, or wiring problem (cut wires or other "open circuit" issues). Changing the radiator may have caused the sensor to be bumped, or the wiring for this sensor to be damaged. An open circuit for this sensor would send engine management a signal for "very cold conditions", requesting a rich fuel mixture - resulting in rough idle, and black smoke from unburned fuel. I would suggest a engine sensor inspection by a mobile, professional mechanic, such as one from YourMechanic, who will come to your location, diagnose this problem, give you an accurate assessment of damage and cost estimate for repairs.