I may be going back to Mobil 1 on my next oil change for the Exmark. The Rotella T6 seems to be working for the diesel truck and the Goldwing. I had soot problems with the diesel truck before going to Rotella. My turbo vanes "coked up" 2 times in 36,000 miles when using dino oil. Maybe the Rotella helped or maybe it was just luck. I have been 37,000 more miles without any problems.