I assume that you created this post because the thread title is more approprate than "Changing my PTU Fluid".
I'll try not to retype anything that I've already written in that thread. (the key word is try
Just so I understand your question correctly, you are saying that by disabling the PTU and rear wheels, you are essentually "towing" your rear drive train. If so, that is a very good point and then you for posting it. If not, could you please explain what you are asking?
Assuming that my understanding of your question is correct, this is how I see everything working and I'm sure there are some who will disagree with me but that is the reason for these message boards, to debate ideas.
With the fuse pulled, what is being done is removing torque from both the ICE (Internal Combustion Engine) and electric motor to the rear wheels. Everything still spins, the rear clutch is just never commanded to engage.
Now some may argue that because of the fact that everything is still spinning that there is nothing to gain from keeping torque from going to the rear wheels but there is a gain from the reduction of friction. Every joint and gear creates heat from friction as it spins. When the force is changed, (the torque from the engine) the friction is increased. When the work is increased (the inertial resistance caused by the weight of the vehicle, Newton's laws of motion) the friction is also increased. By keeping torque from going to the rear wheels, there is no work being done by these gears and u-joints of the rear drive train other than the work required to turn them because the rear wheels are turning. Therefore the work done by the engine is less due to less friction and heat being generated.
But, because everything is still spinning, all of the systems are still being lubricated. Removing the fuse and disengaging the PTU is the same as driving 1,000 miles at 55 mph
over flat land. All of the torque would be applied to the front wheels and the rear wheels would essentually be towed holding a constant speed. I live in an area with a lot of hills and my PTU failed because torque is being applied 40% of the time to the rear wheels which caused the PTU to overheat (construction season didn't help either
I understand what you are saying with the lubrication but I believe everything is still rotating and getting its proper lubrication so it is nothing to be worried about but if others have greater knowledge of this, please feel free to correct me. (corrections seem to be a abundant on this message board