You can buy the 0W40 at any wal-mart, so I'd just keep using it. The 5W40 I have seen is for diesels though I think I heard they started making a new one for gassers too...don't know what difference it makes but if you've been using the 0W40 all along why switch now? Save a couple of bucks a quart and buy it at W-M.

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Marty D.

2013 C300 4Matic
1984 BMW 733i
2013 Lincoln MKz