Why does the viscosity of car oil change with temperature?

Answer 1

yes...lower temperature ..higher viscosity
they use to have different oils for winter and summer just for that reason.

Answer 2

Look at viscosity in terms of "thickness" or "density". As the oil heats up with engine temp the molecular makeup expands, spreading the molecules apart. It could be said it spreads the thickness or density out making it thinner or less viscous.