Truck Repair: s60 engine, fan clutch, fuel mileage

Question
I have a 2007 freightliner century with a Detroit series 60 engine. I hear an air release type sound when the turbo kicks in under high torque, like pulling a grade,or pulling a heavy load. Im wondering if the turbo is going bad or could it be something else. I started hearing this sound after the outside temperature hit 80 or above for a couple days in a row. and my fuel mileage remains the same.

Answer
Could be a couple things your fan is air operated so could be your fan is leaking air best way to check that is shut the truck off and then turn the key back to the on position give it a minute and if you hear air around your fan clutch it will need rebuilt. But more then likely what i think your hearing is when your pulling grade and heavy loads your turbo has a waste gate that opens up to keep from building too much boost would say thats what your hearing. Doubt the turbo itself is going bad but the actuator controlling the boost could be. On the good side thats not much to worry about will need changed eventually but nothing to shut down over real quick. on the bad side you can buy the actuator on them but to keep you from buying them they have priced them a few dollars less then just buying a new turbo with it on there.