Will, why wait until the Starmark Warranty runs out to switch to Mobil 1? Start using it immediately. If you're in NC 15W40 oil should be fine for year round use. Check the oil weight vs. outdoor temperature chart in your Owner's Manual to confirm that it's OK. Realize that the dealer isn't going to service customers' cars with an oil that will cause problems during the winter months.

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Fred Hoelzle