leftydog,
Just to add something from my Honda experience...
Honda's seem not to like any coolant with silicates, borates or phosphates. And that's what Honda specifies for their coolant. Not wanting to pay $18 for premixed coolant, I did some research and found that Zerex Extended Life is ok for Honda cooling systems because it is free from the above particulates. So I'd think it would be ok for the Nissan, but I haven't researched it yet.
From what I understand, it's the regular old prestone with it's phosphate rich formula that attacks the soft metals over time. This isn't really an issue with a cast iron block and head, but when you get into alloys...hmm.
As far as mixing the two types, I don't see a problem. They are both ethelyne glycol based. I went to NAPA to pick up a few gallons of the Zerex and the counter guy cautioned me NEVER to mix the two, implying something just shy of a vortex to hell would open if I did. I asked why and he said the extended life stuff isn't made from ethylene glycol. So, I had to show him where it stated just the opposite on the container... :rolleyes:
In any case, get as much of the old stuff out as you can out of there using the Nissan directions as rb42 mentions and make sure you use distilled water. Unless you have extremely soft tap water, don't let it come near your cooling system. Additionally, you should perform this service once every two years.
One other note. What you're looking for with modern vehicles is something that won't attack soft metal, hence the silicate, borate and phosphate free requirement. When you go shopping for some coolant, the parts people will often ask what color you want...whic in this case is actually irrelevant as some Dexcool type stuff does have silicates. Regardless of how "long life" the stuff is, I'd still change it every two years. This stuff does break down over time and become more acidic...
Bogatyr
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2001 Nissan XTerra XE 40k
1984 Honda CRX 1.5 83k
1970 Land Rover IIa 88" 41k
1966 Land Rover IIa 109" 35k