I am reading a 2010 Subaru owner's manual, it shows a chart of recommended engine oil viscosities for a given ambient temperature range. For cars operating in temps above -5 degrees Fahrenheit it recommends using 10w-30, 10w-40, or 10w-50 oils.
About 90% of US drivers fall into this category,
99.9% of the time.Why is it that so many people decide not to follow this recommendations and pour oils of 5w-30, or
5w-40 viscosities?The manual shows a second chart where 5w-30, and 5w-40 are shown along the entire temperature spectrum, from less than -20 to above 100 degrees F. Meaning these oils are also permissable, but they are not a perfect match!
I do not understand the logic behind the use of these thinner oils. Do people no longer care about their engines, and prefer a thinner oil for better fuel efficiency alone. Why then stop at 5w-30, and not pour 0w-30, or 0w-20, or even thinner (0w-10 will soon be available).
Basia