TimVipond, there's no way I can back this up with proof (it's long gone) - but I have perused the Mobil 1 web site for many a year - from Tri-Syn days to Super Syn days. And - "back in the day" (seven to eight yrs ago) - in the FAQ section, Mobil 1 made mulitple statements for which I'll here paraphrase a typical Q&A -
User - "Many American and European car co. are now advising very long OCIs - some as high as 18k, will M1 handle these OCIs"
M1 - "We recommend you always follow the OEM OCI, and you can be very confident that M1 is more than capable of handling these OCIs" (and these were in reference to the entire M1 line - not just 0w40).
Also note that Mobil 1 used to guarantee their M1 product line for 25k or one year (I believe this was the case thru the '80s and early '90s). Then they backed off this. They were still answering questions on this seven or eight yrs ago - there answer was something to the affect - "we wanted to stay consistent with the OEMs recommendations, though M1 is quite capable of going above and beyond these".
Then, around 1997 when I was flirting with leaving Amsoil due to shipping charges (and I did leave), I called M1 (really!) and told them I did 25k/yr and asked if I would be ok with M1. The technician told me they could only state that M1 was recommended up to 15k OCIs. Then I told him it was mostly hi-way, etc, and he said "we only only state 15k, but you will be fine."
So, historically, with the EP line, M1 has simply once again put the warranty on the bottle. But 15 to 25k has always been the stated (whether on the bottle or on their web page (though sometimes buried in their FAQ sections) OCI assured for the full M1 product line.
However, now that they've once again stated it for EP, who knows if they might reformulate some of the reg. M1 line to be less than 15k oil (??).
