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C7 Diff oil?

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Old Jun 18, 2018 | 08:32 PM
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Default C7 Diff oil?

Hi all,

Is the recommended C7 differential fluid weight the "LS" 75w-90 gear lube?

Assuming so, but the OM is pretty vague... just says "Dexron LS", with no viscosity spec given. I have yet to see Dexron LS in anything except 75w-90, but I do see "Mobil1 LS" in both 75w-90 and 75w-140.

Anyone use or recommend the heavier 75w-140 in their street-driven C7? Does the standard diff/e-diff equipment make any difference?

(My preference is always towards Mobil1 products, and in my C6 days, it was believed that Mobil1 LS and Dexron LS were, in fact, the same oil in different labels, and that Mobil1 actually manufactured the LS product for ACDelco.)
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Old Jun 18, 2018 | 09:45 PM
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Somewhere in the OM I believe it also gives part numbers for the fluids, you should be able work backwards from there to find the viscosity.
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Old Jun 18, 2018 | 09:57 PM
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Originally Posted by Kent1999
Hi all,

Is the recommended C7 differential fluid weight the "LS" 75w-90 gear lube?

Assuming so, but the OM is pretty vague... just says "Dexron LS", with no viscosity spec given. I have yet to see Dexron LS in anything except 75w-90, but I do see "Mobil1 LS" in both 75w-90 and 75w-140.

Anyone use or recommend the heavier 75w-140 in their street-driven C7? Does the standard diff/e-diff equipment make any difference?

(My preference is always towards Mobil1 products, and in my C6 days, it was believed that Mobil1 LS and Dexron LS were, in fact, the same oil in different labels, and that Mobil1 actually manufactured the LS product for ACDelco.)
Yes, the factory spec is 75w-90. The mobil 1 LS 75w-90 is a full synthetic and a great choice for a diff oil change and has the friction modifier additive in it.

Last edited by BJ67; Jun 18, 2018 at 09:58 PM.
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Old Jun 20, 2018 | 05:40 PM
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We use the Royal Purple 75w90 with great results on both street and track day applications.
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Old Jun 20, 2018 | 06:20 PM
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Available on Amazon.
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Old Jun 21, 2018 | 02:27 PM
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Originally Posted by Kent1999
Hi all,

Is the recommended C7 differential fluid weight the "LS" 75w-90 gear lube?

Assuming so, but the OM is pretty vague... just says "Dexron LS", with no viscosity spec given. I have yet to see Dexron LS in anything except 75w-90, but I do see "Mobil1 LS" in both 75w-90 and 75w-140.

Anyone use or recommend the heavier 75w-140 in their street-driven C7? Does the standard diff/e-diff equipment make any difference?

(My preference is always towards Mobil1 products, and in my C6 days, it was believed that Mobil1 LS and Dexron LS were, in fact, the same oil in different labels, and that Mobil1 actually manufactured the LS product for ACDelco.)
75w-90 and will be the right one
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Old Jun 23, 2018 | 05:21 PM
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Wait, the Mobil and Redline have the additive already?
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Old Jun 23, 2018 | 05:40 PM
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Originally Posted by village idiot
Wait, the Mobil and Redline have the additive already?
The Mobil1 LS does for certain. Not sure about Redline.
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Old Jun 24, 2018 | 06:00 PM
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Originally Posted by village idiot
Wait, the Mobil and Redline have the additive already?
Not sure about those two, but as you probably know already, the GM fluid also has the modifier.

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Old Jun 24, 2018 | 06:02 PM
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Originally Posted by Gearhead Jim
Not sure about those two, but as you probably know already, the GM fluid also has the modifier.
Mobil 1 LS 75w-90 full synthetic has the friction modifier additive.
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Old Jun 24, 2018 | 11:11 PM
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AMSOIL on all my stuff.
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Old Jun 25, 2018 | 03:03 PM
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Originally Posted by Gearhead Jim
Not sure about those two, but as you probably know already, the GM fluid also has the modifier.
Correct. I assume the LS stands for limited slip for differentials.
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Old Jun 25, 2018 | 06:33 PM
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Originally Posted by TEXHAWK0
Correct. I assume the LS stands for limited slip for differentials.
I believe you are correct.

IIRC, the "LS"-labeled product (both Mobil1 and GM) was introduced to help eliminate the C6 posi clutch chatter issue.
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