RedLine 75W-90 GL-5, 3k mi OCI, 37k mi

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All mileage is in kilometers not miles. Switched to fill of RedLine Heavy ShockProof since mechanic said the fluid looked bad at pre-track inspection.

The previous fill was: "SAE 75W-90 Synthetic Axle Lubricant (GM Part No. 89021677, in Canada 89021678)" (quoted from manual)

Plan going forward in about 3 months and 3k miles (and 11 track days later), switch back to RedLine 75W90 for the winter, thoughts on that?

The report below has 2 track days on it and it had 4oz of GM limited slip additive added (even though it comes already with additive to combat chatter experienced by others with similar diffs):

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800+ iron in the previous sample?

the 300+ could be mostly from residual oil.

I expect next change no matter how severe the usage will be lower.
 
What's the color (or smells,if any) of this used sample in amberish/grayish/brownish hue ..... pictures ?
Appreciate if you could share here RL's comments ....... particularly on drastic drop in flash point which I would consider as abnormal.
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I didn't take a picture, but it looked rather darkish in the sample bottle. I'll let you know once I have RL's comments. Drastic drop? That was a different oil that had thickened up. Wouldn't you have expected the flash point to have gone up then?
 
Quote:
800+ iron in the previous sample?
the 300+ could be mostly from residual oil.
I expect next change no matter how severe the usage will be lower.

I would estimate an average of 100 ppm Fe (from a range of 80 to 120 ppm) was carried forward to current sample from previous residual sample, hence guesstimating that the current 3000 miles OCI 'creates' another 280 ppm or so of iron ...... which is a red flag and alarming , as far as I'm concerned.

Originally Posted By: Emperors6
I didn't take a picture, but itlooked rather darkish in the sample bottle. I'll let you know once I have RL's comments. Drastic drop? That was a different oil that had thickened up. Wouldn't you have expected the flash point to have gone up then?

I mean from virgin flash point of 440*F (or 430*F for Red Line NS version), it drops to 390*F in 3000 miles.
Is it a Red Line non-NS version ?
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It's RL 75W90 GL-5 LS (with the limited slip additive), and then my mechanic added another 4oz of GM's limited slip additive for good measure due to chatter he's heard from other similar rear diffs.
 
Originally Posted By: Emperors6
It's RL 75W90 GL-5 LS (with the limited slip additive), and then my mechanic added another 4oz of GM's limited slip additive for good measure due to chatter he's heard from other similar rear diffs.


In a mere 3000 miles OCI for this RL GL5 :
a )KV@100*C drops by about 10% from 16.4 cSt;
b )Fe counts (after less residual ppm) of about 280 ppm additional; and
c )Flash point drops by 50*F from 440*F
.......... I'm beginning to doubt my previous suggestion (in the other thread) of 75W140, would not be adequate after all, for this CTS application.
Btw, what's OEM recommended OCI for this diff which you mentioned as 'short'?
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The OEM doesn't specify any OCI for the differential that I could find. When I said short I was thinking of going at least 6k miles before changing it (i.e. 6months).

So, what should I run in the winter then if you can't even recommend the 75W140? I've read that the Heavy Shockproof has gelling concerns in winter and I will be seeing -10C regularly (and maybe -20C occasionally). It doesn't seem like a good idea to keep it for the winter. I'll replace it anyways so I can sample it.

I'm curious what Dave @ RL will say.
 
You mean those that get tracked? No idea, it's up to the individual. I've read some people change it out after every event, while others once or twice a year.
 
A 75W140 would shear more than a 75W90 whilst I consider your requirement to be a 140 or higher viscosity grade. Hence I would rule out 75W140 in the CTS.
80W140 is good for -26*C(-15*F), hence suitable for winter use.
In summer, for mineral I would assess whether 85W140 performs better than the 80W140 and......
for synthetics that I can think of now, Amsoil SAE 190....
you may have other suitable products that possibly performs better than a 80W140 in summer.
 
Originally Posted By: Emperors6
You mean those that get tracked? No idea, it's up to the individual. I've read some people change it out after every event, while others once or twice a year.

What about non-track OCI by OEM ?
 
I would rather stick with RL (same chemistry) in the summer and non-summer. What do you recommend then?

No track or non-track OCI. Let me double check if it's anywhere else.
 
The manual for the 3rd gen CTS-V says to replace rear diff fluid every 72k km. Plus, to change it when driven in severe or competitive conditions.
 
what did you put in now, still the shockproof? I would run another 5000 miles and see what the iron does. There's no way of knowing how much iron is left over from the previous fill, or how much old fluid got mixed with the new.

Also, don't add any LS-additive until you get chatter...

If the diff is already damaged, not even the best oil in the world will save it.
 
Just to be clear, this UOA is for the RL 75W90 LS (with another 4oz of LS additive (GM's one) added). Then, I put in the RL Heavy Shockproof, and will change out and UOA in late Oct/Nov this year to see how it compares.

Dave's reply:

"The flash point is a little lower than expected, likely a variation in test procedure, the viscosity is lower than original and the TAN is much higher than expected, so likely a good idea to change it. The iron wear metal is continuing higher than expected, though may be normal for your differential.

The ShockProof doesn’t contain as much friction modifier as needed to control chatter from a clutch type limited slip on the street, but would provide additional lockup on the track. Additional friction modifier will reduce the lockup of the limited slip clutches on the track.
"

I've asked Blackstone to re-run the viscosity, TAN and flashpoint tests if possible to make sure.
 
Originally Posted By: Emperors6
Dave's reply:
"The flash point is a little lower than expected, likely a variation in test procedure, the viscosity is lower than original and the TAN is much higher than expected, so likely a good idea to change it. The iron wear metal is continuing higher than expected, though may be normal for your differential.

Dave has the highest respect from me for his honesty, truthfulness and professionalism .......
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