Originally Posted By: HighViscosity
I just don't understand how an oil can go that long without corrosive damage. The TBN would be depleted long before the oil change, and you would be running acid oil.
Low-sulfur fuel, like we will have in the US come 2017, minimizes acids formed during combustion. Long changes have been the standard for some time in Europe.
A good, physical example of this is the BMW N63 engines. In Germany, a variable Service Interval Minder based on fuel consumption and other parameters would allow for an OCI of up to 2 years or 30,000kms on LL04 low-SAPS oil. The same interval in the US resulted in many grenaded turbos, slack noisy timing chains with broken guides, and clogged/damaged VANOS units, prompting full rebuilds under the Customer Care Package and a shortening of all BMWUSA OCIs to 1yr/12k miles with LL01 full-SAPS oil.
Moving towards low-sulfur fuel and low-SAPS oil in the Unites States will enable greatly extended OCIs, as well as help minimize some of the more common problems with Direct Injection: carbon buildup in intake tracks and on the back of valves.