T4 is 15w40 "conventional" and T6 is 5w40 synthetic. I've been using T4 for a while without any problems except hard starting at lower ambient temps. I've used T6 before and the starts are good but shifts are quite notchy. My idea is to blend T4 and T6 50/50 to get a 10w40 that is really stout and really affordable... looking for a middle ground I guess. Your thoughts?