The Nissan Path

And do they react badly with one another?

My Mechanic ( whom I generally trust quite a bit) has neither in stock and feels one of his other fluids will do well..

Thoughts?

Nissan Long-life green anti-freeze, which is actually Pentosin Pentafrost A2 anti-freeze, was used in all Nissan vehicles until Nissan Extended Life Blue coolant, which is actually Pentosin Pentafrost A3, started to be phased into the 2010 model year Nissans. Nissan green comes as a concentrate, which needs to be mixed 50/50 with distilled water, has an initial service interval of 90,000 miles and then should be replaced every 60,000 miles. Nissan Blue comes only as a pre-mix, thus no water needs to be added, and has a recommended 105,000 mile service interval, although it actually has a 135,000 mile service life. Both are "HOAT" coolants. Nissan Green and Nissan Blue are fully compatible with each other, however, any Nissan Green coolant added to Nissan Blue will decrease the service life.
I've noticed Pentosin products are starting to be carried at some major auto parts stores. I've seen Pentosin Pentafrost A3 (Blue) stocked at my local Autozone store. So, if you are under 135,000 miles, you still have time if you want to stick with the original coolant. Your local auto parts store should be able to get Pentosin Pentafrost A3; you'll need 2-gallons for a drain and fill.
If you can't get Nissan Blue or Pentafrost A3, Prestone offers Prestone 50/50 Prediluted Antifreeze/Coolant formulated for Honda/Nissan Vehicles
(Antifreeze/Coolant PN: AF6300). Other brands have options, as well.

Thanks!!!