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I changed the diff fluid in my base C6 back in 2010 at 8,000 Miles, using GM
Dexron LS Gear Oil 75W-90, part #88862624 (#88862625 in Canada). It came out immaculate.
Now at 45,000 Miles, I will be changing it again.
I have been looking at the 'Valvoline FlexFill Full Synthetic SAE 75W-90 Gear Oil, 946-ml#028-0219-8' and wondering if this is a better choice as it is a Full Synthetic oil.
Is this a good idea, or should I stick with the GM stuff ? If I do go with the Valvoline, would there be issues as there will be some of the old oil mixing with the newer synthetic oil?
I know you can mix non-nsynthetic with synthetic engine oil, so my guess is mixing won't be an issue. Perhaps the GM oil is in fact synthetic ??
Thoughts ??
Thanks,
M
Last edited by Mike Green9; Feb 10, 2026 at 12:57 PM.
Reason: typo
GM fluid is synthetic and has proper amount of friction modification additive.
Aftermarket fluids typically don't have the additive and it must be added separately. Some forum posts of people using aftermarket fluid and having diff chatter issues.
GM fluid is synthetic and has proper amount of friction modification additive.
Aftermarket fluids typically don't have the additive and it must be added separately. Some forum posts of people using aftermarket fluid and having diff chatter issues.
There are just as many fluids with LSD additive in them now as without.
IMO, just use whatever is the right weight, and either has LSD additive, or add it yourself if it doesn't.
Changed the Diff fluid in my Dad's '07 last summer. Used Valvoline in the convenient squeeze packs. Bought an extended fill spigot which made the operation a breeze. All items purchased at O'Reilly.
I changed the diff fluid in my base C6 back in 2010 at 8,000 Miles, using GM
Dexron LS Gear Oil 75W-90, part #88862624 (#88862625 in Canada). It came out immaculate.
Diff Fluid Recommendations
