The SAE (Society of Automotive Engineers) defines degrees of viscosity for lubrication oils under high and low temperature conditions.
- The figures preceding the letter W (winter) indicate fluidity at low temperature. The lower that figure, the more the oil flows when cold.
- The figures after the W indicate the viscosity at high temperature. The higher the figure the more viscous the oil is when hot.
Single-degree oils (5W, 10W, 15W or 20, 30, 40, 50) have been replaced by multi-degree oils (5W-40, 10W-40…) to respond to the needs of present motors, as multi-degree oils combine service at high and low temperatures.
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