Originally Posted by AzSpeng

I can see a reason for needing a higher pressure and thats what the cap on the actual coolant system (taking the reservoir out of the equation) is for.The whole purpose of the tank is that when the system heats up and the main cap releases pressure, the coolant has to have a place to go, hence the reservoir. When the system cools the coolant is "sucked" back into the system.

So raising the pressure of the main system (with or without a reservoir) has no effect whatsoever on how big, what style (pressurized or non) of reservoir tank being used.

That is my take thus far on a performance standpoint, I dont think that it matters. NOW! this is my take on a possible reason WHY 'they may have changed and to me seems the most logical right now.

With a non pressurized you are relying on the main coolant system to overlow at certain pressures into the vented tank. As the system cools the system sucks the coolant back into the radiator. Perhaps Nissan found that there was not enough "suck" force to get the required coolant back into the system and thats why they changed to the pressurized system?

The pressurized system would always have some degree of pressure which would force the coolant back into the system as the system cooled instead of relying on what vacuum forces the cooling system had to offer at the time of cooldown.

That is the ONLY good explanation I have at this point in time.

Would you say you agree or disagree? What are your thoughts?