Full Floater Posted December 1, 2023 Share Posted December 1, 2023 Any reason not to run 75w-140 in a 6 speed? One of mine is well worn out and is hard to shift when hot. Shifts good when cold (think oil) but i'd like to put something in it with a higher viscosity when at operating temp. So I was thinking 75w-140 and some Lucas. Quote Link to comment https://www.bigmacktrucks.com/topic/73598-75w-140-in-a-6-speed/ Share on other sites More sharing options...
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