I have an '05 Jeep Liberty with the diesel that I have been quite happy with for the past year. I'm about to turn 9K miles. The REQUIRED oil as per the owner's manual is M1 0W-40 (with M1 5W-40 being the only acceptable substitution). I am pretty sure the OCI is 12K miles. See this link for the manual specifics. I know that the quality of this oil is unquestionable, but it's suitability to this application just does not strike me as "ideal". The oil on the dipstick looks absolutely carbon black, and will even stain your hand if you get any on your skin to the point that it is difficult to remove. I know that diesels run "dirty" and that how the oil looks is not an indication of a) it's suitablity to an application, and b) it's need to be changed. This oil is also API rated for diesels and meets the stringent Mercedes Benz (diesel?) spec. 228.? Probably partly because I use the vehicle hard with some towing in the 3K to 4K range (it's rated for 5K), lots of short trips, and lots of hauling, I can't help but think I'd be better off with shorter OCIs and a diesel specific oil like DELO 400 15W/40. While the M1 seems to be primarilly a gasoline engine oil that also happens to be rated for diesels, the diesel oils are primarilly formulated FOR diesels that also are rated for gasoline engines. I would think that the diesel specific oild would better be able to deal with the soot and other by products of diesel combustion. I personally think that Daimler-Chrysler engineered the CRD with every fuel mileage increasing trick in the book because that was to be a major selling point for the vehicle....and one of the reasons I bought it. Specifying this oil in this grade smacks of this motivation. Another example is their tire and wheel choice for the CRD's....they ONLY come with the lighter alloy wheels and some very unimpressive skinny (low rolling resistance) Goodyears that were so bad in the wet when the turbo kicked in, that I replaced them at 800 miles. Anyway, I did an oil/filter change at 5000 miles and stuck with the "required" M1. I'd love to at least be able to try something different but fear messing with the warranty. Any thoughts?