SAE Viscosity Grade
Viscosity is a measure of an oil's flow characteristics, or thickness, at certain temperatures.
The low-temperature viscosity (the first number, 10W in 10W-50 oil) indicates how quickly an engine will crank in winter and how well the oil will flow to lubricate critical engine parts at low temperatures. The lower the number the more easily the engine will start in cold weather.
The high-temperature viscosity (the second number, 50 in 10W-50 oil) provides thickness, or body, for good lubrication at operating temperatures.
SAE 10W-50 provides good flow capability for cold weather but still retains thickness for high-temperature lubrication.
