The point of swithing to synth oil is to avoid the wear and tear on the engine... It doesn't break down as easily as Dino oil, and protects your parts from wear for longer... If you've run you engine that long on Dino Oil, you've probably got allot of wear allready... but you can switch it if you like.... They just don't suggest switching back and forth between the.... IE, Dino one 3k, and Synth the next 3k, and back to Dino.... If your going to switch, stay with Synth, At least it will help with further wear....