Because motor oil does not crystallize, or solidify, at any temperature, it technically does not freeze. However, motor oil at freezing temperatures will begin to thicken, losing the viscosity that allows the oil to flow throughout and lubricate the engine. This increases the risk of damage to engine parts in cold weather.
Because oil is a petroleum product, it will not freeze solid in cold temperatures, though it will lose its liquid qualities as temperatures fall. For example, diesel oil that is cooled below 0 degrees Fahrenheit will change in color and texture, becoming whitish and solid to the point that it will not flow through the engine. This change is the result of the precipitation of dissolved waxes contained in the oil. Gasoline does not contain these waxes, which is why it is not as sensitive to cool temperatures as petroleum-based motor oils.
To avoid engine trouble caused by thickened motor oil, choose a lightweight, winter-grade oil in the cold months. Lighter oils flow more freely in cold conditions, whereas thicker oils may have trouble moving through the engine, and even prevent the car from being able to start in the colder months. Information about the viscosity of oil can be found on bottle's label. Oils that are suitable for winter driving are marked by the letter W in the oil's title.
Another solution to this issue is to use synthetic oil, which, according to the motor oil manufacturer Mobil India, has shown resistance to thickening in cold temperatures as low as -40 degrees Celsius. On the other hand, crude oil will become quite thick and tar-like as it is cooled