The variations in recommended oil change intervals has perplexed me for some time and I haven't seen any explanation as to why there is a difference. If I've missed the reason previously explained, my apologizes. If there has been none, can anyone shed some light on why there is such a disparity? Without any difference in the combustion components, I can't see that US-based cars would foul oil any faster than elsewhere. Similarly, its hard to believe that US fuel blends would cause oil contamination at twice the rate of the UK (for example). Similarly, I doubt oils commonly used in the US are different (if at all) than those used elsewhere. The cynical half of me thinks Porsche North America might have shortened the interval to provide additional business to US-based dealers :|.