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Hi All,

I know that the owners manual for my 08 Envoy recommends 75W90 in the rear diff, but AutoZone is having a 1/2 price sale on Valvoline 75W140 right now.

My Envoy has 160,000 miles and I bought it to tow my 3,000 pound boat.

Will it harm anything to use the 75W140 ?

Thanks !!
 

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That 90w Gear Oil is recommended for a reason that was determined by engineers so I would be hesitant to use a heavier weight unless you want to blow out some seals. Good luck.
 

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If you use a pure synthetic it won't matter. The SAE viscosity rating system is worse than a bad joke. Convert to SUS or ISO viscosity, select the proper fluids, and never look back.. Not even the lowest of the low-tech industries uses an SAE rating system, except for the automotive field. It simply baffles me that the 120 year old meaninless and arbitrary rating system has been clung onto for so long.
 
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