I have been using synthetic 5w30 in my 05 Civic that calls for 5w20. I figured it would help to protect the engine a little better at the cost of a negligible fuel economy loss. I see no reason why it would hurt. I understand that it was designed for 5w20, but I heard that the only reason that all the manufacturers switched to thinner oil was for fuel economy and not engine protection. What would you suggest for engine protection? Maybe 0w30 for lower start up viscosity and faster circulation in cold weather than 5w30? Any opinions welcome.
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