ONE of the studies I referred to up above, directly comparing synthetics against dino oils in extended drain service is printed by SAE International - it's their publication #952553, the copy I hold in my hands is a reprint from Engine Lubricants (SP-1121)
It's far too lengthy to try to type and post here - and I haven't yet tried the SAE website for the original. IN that detailed article, which was specifically written to display the benefits of synthetics, both in normal and extended service, they compared their chosen synthetics against several control oils refined for diesel use.
While the document clearly shows the synthetics superior in MOST areas of testing in extended drains out to nearly 65,000 miles, it ALSO shows the standard dino oils perform well out to nearly 35,000 miles as well, and actually BETTER than synthetics in some test areas - the engines used in testing were a mix of Cummins, Catterpillar, Detroit Diesel and Mack...
The dino oils used in the test at the time were CG-4 and CF-4 rated oils - the test is dated Oct. '95 - current spec oils now on the shelves for our diesels are CH-4 and CI-4 rated oils - what effect that might have today, as compared to competing synthetics is impossible for me to say - I would imagine the synthetics makers have been improving their product as well...
One item of particular interest in that study, was that out to the maximum mileage of 40,000 miles they used the dino oil, it held steady at *20% LOWER* iron content for the CG-4 dino as compared to the synthetic - makes ya wonder how that translates to engine life over the long haul for those using extended drains with synthetics, doesn't it...
WILL we ever see a million-mile Cummins using synthetic oil and extended drains?
The issue is NOT whether the synthetics will perform better in EXTREME climates, OR whether they will outlast the dino oils in extended drain intervals for those wanting to do extended drains - only to illustrate that the dino oils are ALSO capable of FAR longer run times than most of us use them, and counter the myth that synthetics are the only way to extend oil drain intervals...
And one more time, for MY money, use and climate, Delo 400, changed at about 7000 miles, along with my bypass filter suit ME just fine...
YMMV!
