The ease of starting an engine depends not only on the condition of the battery, ignition and fuel quality, but also on the flow properties of the motor oil. If the oil is too viscous (thick) at starting temperatures, it will impose enough drag on the moving parts that the engine cannot be cranked fast enough to start promptly and keep running.
Wax is a large hydrocarbon molecule that prevents oil from flowing at colder temperatures. Cold, thick oil is more difficult for the engine to pump, resulting in less protection at start-up. Because AMSOIL Synthetics do not contain wax, they remain more fluid at lower temperatures than conventional oils.
Since cold temperatures thicken all oils, oil for winter use must be thin enough to permit adequate cranking speeds at the lowest anticipated temperature and must also be fluid enough to quickly flow to the bearings to prevent wear.