Ive used the 25k mile change intervals and if you buy the Signature series then do the 25k mile interval without worrying. The decision to certify the cheaper oils is for businesses, they dont want to sell the 25k mile oil, they lose money. I honestly couldnt tell you why else, id have to ask. The full SAPS is for use in older models (such as those requiring bmw LL-01) the mid SAPS meets LL-04. The sulfated ash and phosphorus are for the emissions equipment and high performance applications of these vehicles. Most require the full saps, but mid saps works for high performance, the low saps is for the newer vehicles. Also I, as well as Amsoil, recommend that you change early for the first time, from the second change on go for the 25k mile, we do it with the A6 and have had no issues. The 3rd party results were consistant with the in house sometimes the results have been better. Try it and youll see why Amsoil has such a loyal following.

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Do your car and move up to Amsoil.