I use manufacturer oil recommendation on most everything:
2016 Thor Vegas - motorcraft synthetic blend
2014 Nissan Altima - full synthetic
2007 Chevy Suburban - conventional Castrol GTX
All air cooled engines - 15w40 Rotella conventional oil
Chevy small block drag race engines get 15w40 or 20w50 conventional oil.
Neither the Chevy Suburban nor drag motors do well on synthetic, consuption escalates on both drastically. Also seems to leak easier through rear main seals and gaskets. Wear acxeptable on conventional oils.
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