Quote:
Originally Posted by jliltd
I don't know where the misinformation is. The oil system is designed from the get go for specific viscosity range. The galleries and oil pump were fine tuned for this. While I agree going from 0W-20 to 5W-30 isn't a huge difference once somebody starts going extreme like using a 15W they are so far out of the design criteria used for start-up oil viscosity they run the risk of having cavitation in their oil pump at precisely the most important time -- during starting. Subaru's engineers were very specific about what type and weight of oil to use to match their design. Anyting else if "off design".
My experience has been with traditional diesel engines (15W40), piston aircraft (ashless dispersant oil and loose-tolerance air cooled engines) and newer high-efficiency automobile engines such as our beloved boxer. I live in a hot desert and gone are the days of putting good old 15W-whatever into anything that drives up without running into trouble. I have a 2007 Tundra that specifies similar oil (0w30) and I have gotten into trouble trying to second-guess that for our hot and dusty conditions.
I won't stray far from the factory suggestions ever again.
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5w30 is a great idea for certain applications, it has been said before not every decision is made based on maximum performance. Regulations can get in the way.