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Rebuilding subframe on my 04’ M3. Going to swap the fluid out while i’m at it. Would I be able to use this Royal Purple 75W-140 w/ friction modifier additive? What is recommended?
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My Bentley manual says to use BMW SAF-XO synthetic oil. It indicates that the capacity should be 0.9L (0.95 qt). My Bentley does not indicate that the M3 differential is different than the mere mortal versions of the 3 Series.
 

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I believe that your M3 is different, by the way. My manual does not indicate that this is true, and failing to know and understand what might be different can be a fatal mistake for your diff. My belief is that you have a limited slip differential, and the lubrication requirements should be different than for a car with an open diff.
 

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I found this thread. U can use Liquimoly diff oil which already has friction modifiers in it.
Or you can add 4% to 8% friction modifiers depending on the situation.
Go ahead and read The thread it's interesting.

I used Redline 75-140 with no added friction modifiers. Next time I might just use the Liqui Molly version. I am a big Liqui Molly fan
 

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I would definitely go with the oem bmw fluid with fm. I have Royal Purple transmission fluid in my e39 and it works well. But for the differential stick with the oem one. My mechanic went and made an executive decision himself to use Redline and that was a big mistake. Horrible grinding sounds when turning. Swapped it for the oem fluid and my car is much happier now.

 

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I would definitely go with the oem bmw fluid with fm. I have Royal Purple transmission fluid in my e39 and it works well. But for the differential stick with the oem one. My mechanic went and made an executive decision himself to use Redline and that was a big mistake. Horrible grinding sounds when turning. Swapped it for the oem fluid and my car is much happier now.

My experiences are totally opposite to yours. Upon recommendation of Turner Motorsports, who still races E46 M3's, I purchased their package of Redline automatic transmission fluid D4 for my transmission and the differential Redline fluid for my diff.
My car runs smoother and quieter than it did when it was brand new.
I change my transmission and diff fluid every 18 months. Its South Florida, and I run the car quite hard!
I am on my second Redline tranny and diff fluid change now. My 2005 M3 is silky smooth and quiet.
The car has never shifted or felt better. I could not be happier.
 

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It just depends on a couple of factors: Price is usually the first, then where/how you drive.

The factory oil is not louder than the LM (I stock both) but has the correct additive and correct amount of friction modifier for chatter free operation.

Some folks get away with not using the SAF-XO, some don't.
 

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I too had my mechanic use the LM fluid for my diff when i had it resealed a few months ago. Needless to say im spending $150 on the factory fluid as my car sounds awful in parking lots at times. Hoping that should clear it up as its a fairly common problem to find online if you search it.
 

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I opted for the factory fluid. I think this is one area where it's just not worth the anxiety of messing with to save a few bucks. It's not like you change the differential oil that often anyway.
 
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