In the workshop manual ( I don't have the car manual) it says to use 80w90 gl-5 in the diffs and 75w90 gl4 or 5 in the gearbox and transfer. just wondering if it would really matter if I just used 80w90 gl-5 in everything? I live in Queensland, Australia where it is relatively hot yr round. As well I have noticed that a lot of car manuals recommend the heavy diff/tranny fluid for colder temperatures which to me makes no sense. 75w90 would be better for colder temperatures and 80w90 for hotter I would of thought.
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