M6 trans fluid viscosity inconsistencies: OEM vs Dexron III ATFs
 

I've been researching M6 trans fluids threads for a while now in search of potential alternatives to the OEM fluid in my new SS 1LE, mostly because I don't like the cold shifting and nibbling characteristics. I was hoping to find a better cold functioning fluid that could still protect adequately on the track. Along the way, I took note of the point that has been raised by others about the need to look at product data sheets, specifically the viscosity ratings at 40 and 100 c temps. I'm not claiming to be the one genius among us, but I think I just uncovered some stats that have me second guessing the use of ATF in the M6, or if not that, why GM has selected the fluid they have when Tremec says to use Dexron III ATF. Allow me to explain......

Tremec says in the TR6060 data sheet to use Dexron III ATF. Many users have followed this guidance and use their favorite brands (RP, RL, Amsoil, M1, etc). All of those fluids are (I think) full synthetics and pretty much have similar viscosity ratings that are about 36 at 40c and 7.5 at 100c. Redline D4 even has a video on their website where they mention that the Tremec and BMW manual trans have tighter tollerances and therefore need a lower viscosity lubricant such as ATF rather than typical manual trans lubricant.

HOWEVER: The OEM fluid in our M6 appears to have significantly higher viscosity (15 at 40c and 75 at 100c) and is mineral oil, not synthetic. The relatively new Tremec trans fluid is very similar to the OEM in this regard.

This raises two important questions in my mind?

1) If Tremec reccommends a Dexron III ATF in the TR6060, why is the OEM fluid and Tremec's new fluid twice as viscous as the Dexron III ATF fluids most forum members are using (RP, RL, Amsoil, etc)? Is the OEM and Tremec fluid thicker than it should be for the trans design, or are the ATF fluids actually too thin?

2) If we use ATF Dexron III (RP, RL, etc) with the thinner viscosity at the track, are we putting more wear and tare on our trans than if we had stuck with OEM or Tremec's fluid?

Curious to hear others thoughts with respect to the viscosity issues and these two questions. Please don't hijack the thread and tell everyone about your favorite M6 fluid. I'd like to keep it focused on the two questions I've raised.

Well written thread like this makes me miss the “ask Al” days.

Thanks Ninetres.

One slight correction to my original post:
The OEM and Tremec fluids have viscosity of 75 at 40c and 12-15 at 100c (if the scale is linear, that's 2x as viscous as the ATF fluids.

Tremec doesn't recommend ATF in the 6060.


If you read the spec, the data says 'Recommended for motor vehicles with manual gearboxes that require GL4 75W85 MTF, synchromesh, or DEXRON®-III/MERCON® fluids. Not recommended for automatic transmissions or hypoid gear differentials.'


If you compare the specs of the TREMEC fluid to Redline D4 for example, you'll see significant differences. Even basic ones like weight: 75W85 vs 70W80.


My conversations with TREMEC led me to switch to their fluid.


GM wanted a 'one size fits all fluid' so the DEXRON III is close but not optimal in all situations.


Also, which viscosity are you reading? The TREMEC fluid is:
Kinematic viscosity @ 100°C, cSt (ASTM D-445) 12.1
Kinematic viscosity @ 40°C, cSt (ASTM D-445) 71.6


https://cdn.shopify.com/s/files/1/0135/1637/4075/files/specifications.pdf?5237232191582097329

But they do.

https://www.tremec.com/anexos/Litera...et_TR-6060.pdf

The lubricant type is listed by TREMEC as Dexron III ATF. This is a document direct from TREMEC.

And OP, where did you find the specs for the OEM manual trans fluid? This is what I found:

http://apkgroup.com/msds/english/MSD...3-27-2013).pdf

Viscosity @40 C is 34.26 cSt, and @100 C, it's 7.7 cSt. This is pretty close to the other Dexron III fluids.

I have heard that the ACDelco MTF is just Dexron III ATF repackaged.

As for TREMEC HP-MTF, their website said that they specifically made it for aftermarket applications, and while OEM applications can use it, they still recommend you to follow the fluids the car manufacturer recommends.

https://www.tremec.com/not_am_detall...mission-fluid/

I just verified again, straight from the Tremec website data sheet for the TR6060 that the trans lubricant called for is Dexron III ATF.

I agree that the Tremec fluid is heavier grade than ATF (see my posts above in this thread, as I believe we are both making the same point on this), but so is the GM OEM flui (you can pull the current safety datasheet on the AC Delco site as I did the other day). In fact, the Tremec and GM fluids both have about the same kinemetic viscosity ratings at 40c and 100c.

So either Tremec is specifying the wrong viscosity fluid in the TR6060 data sheet (shouldn't say Dexron III ATF as it currently does, and perhaps should call for 75W/85) or the GM and Tremec fluids are incorrectly too viscous for the TR6060 trans and we should be using ATF. Do you know which is the correct answer?

Nice that there is ambiguity where there should be clarity...UnknownJinX linked to the doc that says it all for me...


https://www.tremec.com/not_am_detall...mission-fluid/



The key selling feature of HP-MTF is that it is a product developed for TREMEC, validated by TREMEC, for use in TREMECs. It is intended to provide an ideal balance of protective qualities and shift performance. HP-MTF makes no claim to “outperform” other brands, only to offer assurance to customers that seek a high-quality product that is guaranteed to perform well in their TREMEC transmission.

FWIW, HP-MTF has noticeably, perhaps significantly reduced the operating temps of my TR-6060, especially under demanding load. Full discloser, for me gear temps have never been a concern. I've seen oil temps that have absolutely puckered an unnamed orifice, but even the OEM Dextron kept the gear cool and 100% functional. I love me some TR-6060.

There have been a few posts about notchiness in the TR-6060 in cold climates during warm up. I can't testify to this as I live in a warm climate. For me, TR-6060 has always been buttery smooth when up to op temp.

Expecting optimal performance from any machine when not up to operating temperature is unrealistic and is most certainly mechanically/physically degrading.

You are probably referring to this sheet.

https://public.spheracloud.net/Pdf/1...1753410844.pdf

The part number turns out to be a Canadian part number and is superseded by another part number, 89021806.

https://www.tubmangmpartsdepot.ca/p/.../19354436.html

This turns out to be an ancient GL-3 Manual Transmission Fluid. It isn't even compatible with most modern manual transmissions(which would need GL-4 MTF), let alone TR-6060.

https://www.coloradofans.com/threads...s-stuff.81549/

So this means the SDS I posted in my earlier reply would be the factory MTF. The part number for the stock fluid that comes with our V8 M6 is 88861800, if you want to do some research. It's supposedly just ACDelco's Dexron III with a different name.

https://www.corvetteforum.com/forums...8861800-a.html

In this case, HP-MTF is the odd one out, actually. As noted before, it's not supposed to go into any auto trans, unlike the other Dexron III fluids that can go into auto trans requiring Dexron III.

Upon further checking, it looks like the MSDS I pulled from AC Delco's website was for the wrong product, but it doesn't change my previous conclusions or the remaining questions.

It looks like the current OEM product used in our TR6060 (AC Delco #88861800), which Summit Racing lists as meeting the GM OEM spec 9986252 (the same spec as the 2013 spec sheet that UnknownJinx attached above in the thread) is now a 75W/90 oil. I looked on AC Delco's online catalog and found product #88861800. While they don't have a spec sheet or MSDS for this product, their summary info for this product says:

"ACDelco 75W-90 Manual Transmission and Transfer Case Fluid helps improve fuel efficiency, reduce operating temperature, and improve thermal stability. Gear oil adds lubrication designed to help reduce heat generating friction caused by gear components while also helping provide corrosion protection."

Based on the trans oil weight for the Tremec product (75W85), and Matthew's note above about RL D4ATF being a 70W80, it certainly looks to me like the current GM OEM trans fluid (AC Delco #88861800) is no longer the Dexron III ATF like it used to be and is now more viscous.

So, why did GM start using a thicker fluid than ATF Dexron III in the TR6060, especially when the TR6060 calls for Dexron III ATF?

If we are willing to assume that it's more appropriate to use the OEM 75W90 fluid or the Tremec 75W85 fluid, is the Tremec fluid any better than the OEM? Is is worth 2x the cost?

I am pretty certain that the 88861800 is the same as it has always been, just repackaged Dexron III. Knowing GM, if there is a formulation change, they will probably change the part number to reflect it, along with a technical bulletin to go with it. Heck, they change part numbers for seemingly no reason at times. Just look at the Mobil 1 ESP 0W-40 part number mess if you want to know what I am talking about.

I don't know where you got the viscosity grade from. Perhaps a different part, again?

My thought is this. TR-6060 isn't a new design, by any stretch. It has been used since 2005 and GM has used it for C6 LS3/Z06/ZR1 Corvettes and Gen 5 V8 Camaros. Dodge uses it in the V8 Challengers, and Ford used it for the S197 GT500. A few of these applications are way more powerful than our Camaro SS. If there are issues with the Dexron III fluid, we'd definitely know by now. Look at how long it took for the woes of GM A8 transmissions and Ford MT-82 to spread, then you will know how solid TR-6060 is.

If you want my conclusion...

If you drive mostly for streets, use the Dexron III fluids of your liking. The cold viscosity is thinner, which promotes better flow at lower temperatures. I don't think you can go wrong with the HP-MTF, though. TREMEC is backing it up so there is always that.

If you drive a lot of track driving, the HP-MTF might have an edge due to its higher hot viscosity and perhaps the lower temperature as mentioned before. It makes sense to me as it's initially developed for aftermarket applications of TR-6060, like engine swaps, race use, etc.

I don't have much to add to this informative thread, except to say that kinematic viscosity ratings like this are indeed linear. Kinematic viscosity is just dynamic viscosity (pure resistance to flow) divided by the density of the liquid. The units are mm2/s, so literally the time it takes the fluid to move through a given orifice. Time is linear. So for example, if the Tremec fluid has a 40C viscosity of 75 and a 100C viscosity of 15, then it takes five times longer for a given amount to flow through a given orifice at 40C.

BUMP. Just swung by again to say this debate still seems up in the air. Differing cSt specs in the OEM MTF, the Tremec Fluid, and popular Dexron IIIs, different weight ratings etc. Tremec's literature is keen to constantly cite it's for their "aftermarket" units, and OEM Tremecs should use the OEM fluid.

I'm nearing time for a fluid swap. Switched to Tremec fluid at 1,500 miles. Been great so far at 3,000 miles now and a handful of track days. Not sure what I want to use this time.

Um wow. 88861800 AC Delco is not a Dexron III spec, it is a gear oil spec 75w-90.

See AC Delco site.

I could have sworn 88861800 was a Dexron III spec oil last time I researched this, which is much thinner. I don't know if GM switched the fluids for this part no. 88861800 is what is specified in the Performance Supplement for the ZL1 and in the regular manual for any V-8 Camaro. It has a red tint like Dexron.

There are a lot of options for 75w-90 oils, but synthetics may not be as friendly to the synchronizers.

I looked at my track stats and in a July session here in Austin at COTA (no doubt track temps >110F) the highest transmission temp was 216F. Since oil is measured for viscosity as standard at 100C (212F), that looks fine.

FYI engine oil temps were 275F for three separate laps so that looks like where things are maxing out. Max oil pressure was 71.4psi at those temps (15w-50 Mobil1). Max water temp 223F.