According to the Argonne National Laboratory, petroleum products do not freeze (crystallize), but their viscosity can become very high and adversely affect the instruments they run in, such as a motor. Viscosity is determined by what kind of motor oil or petroleum product is in question and by temperature.
As temperatures increase, viscosity decreases, making oil thinner. This is one reason why crude oil products are useful in automobiles, as the high temperatures of certain components make the oil run more efficiently and smoothly. However, the relationship between viscosity and the type of crude oil product is also dependent upon the other chemicals included in it.