["When my nephew's car broke down and I loaned him my car, I know that he'll be careful with it."]
Well at least you can trust him to be careful.  I dont think I would be able to trust my nephew as he is only 18 and not very responsible yet.
My nephew's car broke down last month and he needs a car to get to work.  His money is tight because he's getting married in the fall and can't really afford to rent a car for a week and a half, so I loaned him mine.  I know he'll take care of it.