I just used Castrol, not even sure what. Conventional or blend I think. it was the only 20-50 they had at the O'Reilly's so I bought it. I'll put less than 100 hours on a year, and will be changing every other season so it doesn't matter to me. I'll use whatever is on hand. If I was planning on 7-10K oil changes in my car like I have done for the past 200K+ i'd use the synthetic and appropriate filter, but otherwise, keep the levels good and change it within specs. works for me