I've always used Mobil 1 or T6 Syn in my MAN CR1550's. Pulled them apart for a major today. 5 years on the after coolers an 30 months on the heat exchanger. I think the after coolers are pretty amazing that they are so clean. One of the benefits of running synthetic oil. Obviously, the oil doesn't matter to the heat exchangers but I'm surprised how clean they are too. About 4 years on the coolant and no build up from it either.