[MJN]

API standards have changed and there is even now a GM Dexos1 Gen 2 specification and are backwards compatible. Typically changes are made for the additive packages and detergents in the oil to prevent breakdown and volatility at the higher temps these new engines run at and especially added stresses of turbo charged engines and direct injection engines. Don't be concerned about using 5w30, remember with a multi-grade oil it will perform as a lower viscosity oil (5 weight) below 32 degrees and a 30 weight at warmer temps. Usually tighter tolerances require a lower viscosity oil so it flows easier into tighter areas, it will take less time for a 5 weight to get to critical areas than a 10 weight. Emissions also plays a key into this and the engine doesn't have to work as hard to pump the lower viscosity oil and will use less fuel. There are some import engines that require 0w16 oil now, 0w12 and 0w8 are even expected to follow.