X2 with lenny. Whatever Ski-Doo recommends has been working for me, 4800 trouble free miles (600 engine). Getting close to 250 miles on a tank of oil makes the oil price worth it. By the way, XPS oil powered all of the Iron Dog sleds last year, all brands (except the 4 cyclers). No failures. And another thing, never pass on the opportunity to fill the oil tank, if the eTech engine goes into the tilt mode oil consumption will increase. 550iq