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What are trying to do here get exemplary milage or save money?

Both, if possible. Running synth provides other benefits, too, although I focused my question down to fuel economy to simplify the thread. Of course, threads wander.
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Now suppose you do oil change every 5000 miles = 20 oil changes.


Royal Purple recommends a change interval of "up to 12,000 miles", but of course you still have to change the filter every 3k. I don't really count the filter factor, because it remains constant whether running synth or dino.

97 Montero SR: Factory rear locker, 3.5 L 24 Valve V6, ActivTrac 4wd (Love it) , 3 way suspension, four wheel disk brakes, 32x11.50 Pirelli Scorpion ATs