On engine oil marked 5w-30, why is the latter number higher than the first. According to engine oil manufacturers sources, the numbers indicate viscosity. 5W indicates a cold engine (winter) and 30 at normal operating temperature. But the viscosity of oil drops when heated, so why is it a higher number?
In: Engineering
It essentially means that, when cold, this oil behaves like cold 5-weight oil. When hot, this oil behaves like a hot 30-weight oil. THink of this as a “scale of runniness”. A set of numbers describing how runny this oil is. That means at low temperatures, it will still flow well because it behaves like a low-weight oil. It also means that, at high temperatures, it will still be able to maintain oil pressure because it behaves like a heavier oil. In short, it will tend to stay about the same “runniness” over a much broader range of temperatures than a single-weight oil.
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