The manual specifically states ester oil, so that is what they should be putting in. So if it's free I say take it, the dealership of all places should not be putting anything in besides what Nissan says to use so if they offered free oil then that's what it should be. Although that doesn't mean that's what they had in mind so if your not sure I would definitely call them out on it, and when they give you that look point it out in the manual... not that you should have to
Otherwise I'm sure there are people on here running probably every other various synthetic out there. I think ester oil is supposed to be extremely light weight oil, but I don't know how much thicker everything else really is. I sure you would be fine with any good name brand oil if that's the direction you decide to go.
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