I run Delvac 15w-40 in my Baby WEN (the 1250 watt version of that one). Just passed 15 hours of run time with an 8 hour run yesterday and seems to be doing just fine. Its still shedding a little metal into the oil, but I just changed it today at the 15 hour mark after having changed it at 1 and 2 hours previously. Still, runs strong with no issues.