Winter does not damage engines while they run. It damages them in the first thirty seconds after startup.

At low temperatures, engine oil thickens. The 15W-40 grade that performs well in summer becomes resistant to flow when temperatures drop below freezing. Oil pumps strain to push thick oil through galleries and up to the cylinder head. Critical components—camshafts, bearings, turbochargers—run without adequate lubrication for several seconds after ignition. Metal contacts metal. Wear accelerates.

Industry data shows that a cold start at -15°C produces wear equivalent to several hundred kilometers of normal driving. The W rating in oil grades quantifies this behavior. The number before the W indicates low-temperature performance: 15W oil remains pumpable to approximately -20°C, 5W to -30°C, and 0W to -35°C. A 15W-40 oil used in a climate where temperatures fall to -25°C leaves the engine under-lubricated during startup.

Manufacturer winter guidelines from SHANTUI recommend switching to lower-viscosity grades before the cold season begins. 5W-30 and 0W-40 maintain adequate flow at startup while still providing sufficient film strength at operating temperature. The oil change interval should follow the manufacturer's schedule—old oil contains contaminants and oxidation products that increase viscosity and worsen cold-start flow.

Startup procedure matters as much as oil selection. Idling for 5-10 minutes after a cold start allows oil to circulate and reach operating temperature before the engine is placed under load. Applying load immediately after startup forces thick oil through the system at high pressure, increasing wear on the oil pump and bearings.

For fleet managers, the calculation is simple. A seasonal oil change costs a fraction of an engine overhaul. Matching viscosity to the climate is one of the cheapest reliability measures available.