At the recent Rendezvous in Roche Harbor, the Volvo representative dodged the question of oil change interval referring only to the operator's manual. That manual calls for changes every 100 hours if sulphur content of the fuel is 1% or greater but 200 hours if sulphur levels are less than 0.5%. US marine diesel sulphur levels were reduced to 15 ppm (aka ultra low sulpher) in 2015. Canadian limits were reduced to 0.1% in 2016. So, there is no reason to change oil more often than 200 hours. In fact, periodic oil sampling (which Volvo recommends) could easily allow extending that interval. This is common practice in big truck fleets. It is sulfates that dilute and change chemistry in the oil. No sulfur longer intervals!
