Tinken
Husqvarna
Pro Class
Piston rings do not make a perfect seal and fuel is let by upon compression and ignition. This fuel is also on fire which aids to vaporizing your crank case oil and heating your torque limiter. The oil recirculation tank cools these gasses, condensing the oil out of the vapor and back to a liquid while re-burning the fuel that may still be in vapor.
Stick with Mobil 0W40 if possible, it has much better protection for your engine than 5W40 and tends to vaporize less. Think of your oil as a coolant and not as a lubricant. Hi flow stainless steel oil filters are a plus. Any oil pressure over 36psi gets bypassed back to the crankcase and you will reach that pressure with 0W40. Since pressure is inversely related to flow, heavier the viscosity, the higher the pressure and the less oil flow you have. If you are reaching your pressure limit with 0W40, think about what is happening with 5W40, 10W40, 10W50, 20W50, etc.
Stick with Mobil 0W40 if possible, it has much better protection for your engine than 5W40 and tends to vaporize less. Think of your oil as a coolant and not as a lubricant. Hi flow stainless steel oil filters are a plus. Any oil pressure over 36psi gets bypassed back to the crankcase and you will reach that pressure with 0W40. Since pressure is inversely related to flow, heavier the viscosity, the higher the pressure and the less oil flow you have. If you are reaching your pressure limit with 0W40, think about what is happening with 5W40, 10W40, 10W50, 20W50, etc.