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Do you recommend a 30K change using full flush (cooler line) or just drain and refill? I have been using Valvolene MaxLife, which is labeled as full synthetic (and I assume that is Group III). My son has a 2000 Maxima which the dealer flushed 29,000 miles ago with their brand, whatever that may have been. I have been thinking of going to Valvoline Dex VI. Would there be an advantage in the way of longer service life with the Dex VI over the MaxLife?
Here is my practice which works for me.
For the PathFinder, which does not have a felt filter element, only a course strainer, I do a pan drain and refill once a year, since it is very easy to do because it has a drain plug.
I use a 1 Liter Graduated plastic cylinder (from any science or chemistry supply house) for measuring and it takes 4.5 L per refill (found that out after much experimentation). Once you find out how much fluid your vehicle takes, make a note of it and get one of these cylinders so you know precisely how much to refill.
In my '08 TrailBlazer, which has a felt filter element, but no drain plug, I pan drain and refill every two years or 30,000 miles with DexronVI.
I think the secret to transmission longevity is in keeping the additive pack fresh in order to fight fluid oxidation, get rid of some insolubles, and keeping the temp as moderate as possible.
I would not hesitate to use Valvoline Dexron VI, but in my area, the GM dealer's DexronVI is the same price as Valvoline and Castrol, etc.
BTW, the Schaeffers stuff is good as well. Buy a five-gallon pail and share it or keep it in the basement for all those upcoming drain and refills.
Whether it is Valvoline, Schaeffers, or whatever, they all have to use an approved additive pack and consistent base oils,