I need to replace my radiator fan shroud and understand that I'll need to drain and remove my radiator (and drain engine block) to do this. I was curious whether I can drain the coolant one day and reinstall a couple days later. Will letting the motor sit (drained) for 24-48 hours promote corrosion in the coolant passages in the motor?

 

You'll be fine

edit: just ensure a good flush of the system.