GXP rear diff. fluid change - Pontiac G8 Forum: G8 Forums - G8Board.com
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post #1 of 17 (permalink) Old 11-30-2012, 06:20 PM Thread Starter
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GXP rear diff. fluid change

Changed mine today(just shy of 30k miles) and went with 1.3qts of Mobil 1 75w90. So far so good, really noticed a difference- seems smoother now. Mine was pretty quiet to begin with, reason I changed the fluid is to keep it that way.

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post #2 of 17 (permalink) Old 11-30-2012, 10:00 PM
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Is it recommended to change diff fluid based solely on mileage or time as well?

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post #3 of 17 (permalink) Old 11-30-2012, 10:31 PM
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Is it recommended to change diff fluid based solely on mileage or time as well?
There is no official service interval for changing the rear diff fluid on the G8 in our owners manual. However, the "Severe service" interval for Camaros is 80,000 km / 50,000 Miles. There is no time interval.

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post #4 of 17 (permalink) Old 11-30-2012, 11:15 PM
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Might want to do more research on the oil used. Our G8 diffs are not the same as the camaro as far as fluid requirements. The G8 spec calls for a specific oil with a carbon additive. Head to the other board and search on Castrol SAF Carbon Mod+. Based on info from that board, there is not a cross reference to another supplier. It may be dated info, but it may be worth looking into. The carbon additive is not the same as the friction modifier that can be added for generic LSD's.

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post #5 of 17 (permalink) Old 11-30-2012, 11:28 PM
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Might want to do more research on the oil used. Our G8 diffs are not the same as the camaro as far as fluid requirements. The G8 spec calls for a specific oil with a carbon additive. Head to the other board and search on Castrol SAF Carbon Mod+. Based on info from that board, there is not a cross reference to another supplier. It may be dated info, but it may be worth looking into. The carbon additive is not the same as the friction modifier that can be added for generic LSD's.
I realize that, I was just using the Camaro for a mileage comparison as an earliest imaginable mileage interval, since there isn't a recommended interval for the G8.

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post #6 of 17 (permalink) Old 12-01-2012, 08:40 AM Thread Starter
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There are quite a few G8 owners that have aftermarket synthetic 75w90 lubes in theirs. I think it actually calls for a 75w85 if Im not badly mistaken.

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post #7 of 17 (permalink) Old 12-01-2012, 09:46 AM
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here is a clip from the GM ESi (courtesy of CP)


FWIW, I looked in GM ESi owners manual and service manual, the only reference to diff lube was above. No weight specification given.

Not saying other oil won't work, it's just not specified by GM. I do suspect, GM would not fill the diff with this expensive stuff if not needed.

As a foot note, while looking, I did see where GM recommends brake fluid flush every two years.

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post #8 of 17 (permalink) Old 12-01-2012, 09:54 AM
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On Alldata it shows for fluid type:

Differential Lubricant Castrol SAF Carbon Mod

IMPORTANT: Both LSD and Non-LSD Differentials use the same fluid.

1.32 QTs

And for the interval:

It does not show anything for the interval in normal and severe service scheduals

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post #9 of 17 (permalink) Old 12-01-2012, 09:57 AM
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What about Holden, do they have a recomendation for the Com.?

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post #10 of 17 (permalink) Old 12-01-2012, 11:30 AM
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They say it's "lubed for life" like the tranny...

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post #11 of 17 (permalink) Old 12-01-2012, 01:10 PM
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What about Holden, do they have a recomendation for the Com.?
I was trying to find this last night. In North America, you can get a PDF owners manual online from just about any manufacturer. But I could not seem to trace one down for the Commodore.

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post #12 of 17 (permalink) Old 12-01-2012, 02:05 PM
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Using 75W90 will work fine in most cases but the dealer can void your warranty on the part for using the wrong fluid. Toyota does it all the time in their trucks...

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post #13 of 17 (permalink) Old 12-01-2012, 04:40 PM
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FWIW, here is the labels of the GM recommended lube. Note the reference towards diffs with carbon linings:


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post #14 of 17 (permalink) Old 12-01-2012, 06:19 PM
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FWIW, here is the labels of the GM recommended lube. Note the reference towards diffs with carbon linings:
So just use this w/o the LSD additive ???

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post #15 of 17 (permalink) Old 12-01-2012, 07:05 PM
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^ correct

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post #16 of 17 (permalink) Old 12-01-2012, 07:50 PM
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^ correct
Cool...thanks !!!

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post #17 of 17 (permalink) Old 12-02-2012, 11:25 AM Thread Starter
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Same with Mobil 1, just put it in. Took 1.3qrt dead on the money almost. Mine is smooth as silk.

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