99vetteran

I switched mine back to dex lll yesterday, don't need any additional problems with the driveline.

Eric D

I learned some very interesting things today about transmission fluids. I’ll post more as I compile the data and have time to write. Some of the more interesting findings, I no longer have a fear of using Dexron VI in my 2000 Corvette T56 6 speed manual transmission. You might ask why. I have found that any current transmission fluid you might purchase can have Dexron III, DexronIII, DEX3, DEX-3 or any other like name on their container, and it means nothing. There isn’t any true Dexron III being produced. The fact of the matter, any of the “universal” fluids you might buy are closer to Dexron VI than true Dexron III. This is part of the reason GM has a special part number for manual transmission fluid, 88861800.

One of the other questions I wanted to understand, why changing the fluid from Dexron III (original fill) to Dexron VI cause the shifting to improve so dramatically. It has to do with the friction properties of the old versus the new fluid. As Dexron III ages, the fluid becomes stickier and directly affects the synchronizers performance. This causes clashing of the gears during engagement. The Dexron VI has special friction modifiers that are more stable over time compared to Dexron III. 10 years as in the case of my C5 is far too long to wait on refreshing the transmission fluid. I know better now! My trans now shifts like it is new.

As mentioned above, more to come, including the topic of damage to the paper blockers with Dexron VI, myth or truth.

C66 Racing

Eric,
I disagree with your assessment and have watching this closely for years. GM came out with Dexron VI primarily to provide a lower viscosity fluid to help lower their CAFE. When they came out with Dexron VI they discontinued Dexron III. Shortly thereafter, many manual transmissions with Dexron VI started failing. Not long after that, they released my above posted tech bulletin indicating not to use Dexron VI in manual applications and re-released Dexron III as a new part number, 88861800. Why they didn't just re-release Dexron III is a little bit of a mystery to me, but read somewhere that it had to do with licensing and contracting. Was easier to them just to make a new part number.

Dexron III has a hot (212F) viscosity of about 7.5 cSt (new). Dexron VI has a hot (212F) viscosity of about 6.0 cSt (new), a drop of about 20% (note that I would not be comfortable with that drop in my tranny). By specifying a better basestock for Dexron VI, GM believes that the VI will maintain its viscosity better (e.g. it will not shear down). Dexron III specs can be met with a Group II or mineral basestock. While Dexron VI specs don't specify a specific basestock, most report that it needs at least a Group II/III blend to meet. Group III is a highly hydrocracked mineral oil that is allowed to be labeled synthetic by the NAD.

In practice, Dexron III does shear down rapidly, and this is confirmed by a used oil analysis report I took on my 06 CTS-V at just over 10k miles when I drained the Dexron III and replaced it with AMSOIL ATF:
2006 Cadillac CTS-V Used Oil Analysis Dexron III vs AMSOIL ATF Transmission Fluid

You'll note from this sample that my factory fill Dexron III sheared down from a viscosity of 7.5 to 5.0 in 10k miles, a drop of about 33%. Ouch, and again - I'm not comfortable with that.

I believe that GM's plan was that while the Dexron VI would start lower (at 6.0) it would stay higher in the long run (e.g. not shear down). I'm not sure what they actually found, but they removed the recommendation for manuals so I suspect something doesn't really work as planned with the VI in manual transmissions.

Though I'm not trying to pitch you on AMSOIL, as an FYI and for comparision with the factory fill fluids (whether III or VI) AMSOIL's ATF and Torque Drive (ATD) use a Group IV PAO basestock that is extremely resistant to viscosity shear down. In the above sample, at that time the AMSOIL ATF viscosity was 6.8 cSt new. After about 7k miles, it was still 6.8 cSt - no change.

This link (and hopefully the mods will let me put it here) shows some of this viscosity shear down I'm discussing from a GM perspective. It also discusses why they discontinued the III and released a new part number as I mentioned above:
http://www.sandyblogs.com/techlink/2...dexron-vi.html

Short story - I would not put Dexron VI in my manual transmission.

ctusser

I've tried Royal purple in two vehicles and Redline in another and the cheap Valvoline DexIII shifts better. I haven't tried Amsoil though.

Eric D

Subdriver,

I guess I’m not sure what you are in disagreement on. If it is about GM Manual Trans Fluid 88861800, you may want to have some analyzed as it isn’t Dexron III nor does it have the same properties. I do know the reason for the technical bulletin and it wasn’t because of transmission failures. You will no longer find that TB in the GM data base. I want to point out that I am not an expert in the makeup of transmission fluids and I really don’t know all of the jargon terms. I do have access to those who are experts that know way more than I. I am also required to state that anything I write is my personal opinion and has nothing to do with the company I work for. That said, I want to pass on some of what I have learned with the hopes of clearing a lot of miss information that I personally ran into.

Even though you claim you are not trying to pitch Amsoil, you are, and I see nothing wrong with that. I’m sure they make good products and their products will do the job they are designed to do. I also believe it is pointless to make any comparisons to Dexron III because it is out of the picture and doesn’t mean anything anymore. No need to maintain a Dexron III license when the product no longer exist.

As far as your Short story, it is your transmission and you can put in it or not anything you feel would be best. For me, the person who authored the article you referenced and have a link too has a different opinion than you. In fact a number of experts I recently contacted see nothing wrong with using Dex6 in my 2000 manual transmission.

The main points I’m hoping people walk away with here, there isn’t any Dexron III and anymore. If your Corvette has its original Dexron III in it, it’s time to change it. If you want, there is no reason to fear using Dexron VI or any other good name brand Dexron VI product.

Subdriver, thanks for your reply..

lucky131969

Eric,
Thanks for taking the time to post, it's nice to have a forum member within GM to obtain factual information. Keep the facts coming

C66 Racing

Eric,
While I agree that Dexron III no longer exists, the fluid spec properties required by Dexron III are the same as GM part 88861800, thus no matter what we really call it, it is the same fluid.

While I certainly don't dispute that the above mentioned Tech Bulletin may no longer exist (I can't verify that one way or the other), what I am less clear on from your posts, and would appreciate more info on is if Dexron VI is, as you state, now backwards compatible for manual transmissions originally specifying Dexron III, then why does GM still carry 88861800?

My opinion, and as you indicated, this is only my opinion, is influenced by GM's own recommendation to use part 88861800 in the Corvette Manual transmission vice Dexron VI. See page 7-10 of the 2010 Corvette Owner's manual as example. GM recommends 88861800 for the manual, Dexron VI for the auto: (this was downloaded off Chevy's website)
http://origin-chevrolet-prod-iad.pna...ble_owners.pdf

It really does not make sense to me that if Dexron VI was, as you state, suitable for a manual transmission, that GM would carry and recommend 88861800.

Eric D

Subdriver,
You are entitled to your opinion. We draw our opinions base on the information we have available to us. Some of my opinions on the manual transmission fluid are based on privileged information and for various reasons are not something I am at liberty to share at this time. I’m working to see if I can change this, but it’s not my decision.

I can tell you that part number 88861800 was part of an agreement and it is not the same as Dexron III. I can also tell you that in regards to my 2000 Corvette manual transmission, Dexron VI is backward compatible. As you may know, my 2000 Corvette is no longer under any warranty. Anyone that has a vehicle that is under warranty should follow the recommendations of the manufacturer to avoid risking warranty issues. As you pointed out from the 2010 Corvette Owner’s manual, owners should use 88861800 until a TB comes out given other choices.

C66 Racing

I think the key point of difference in our opinions was clarified in your post above (that I bolded). I was concerned that readers of this thread could infer from your posting that use of Dexron VI was okay, but I was concerned that there is no open source documentation supporting this view (and appreciate that you are working to get such documentation released). My view is summarized by your last para in that cars out of warranty can really do whatever they want, but cars under warranty, if they want to keep warranty coverage, are much more limited in their choices. And, at least for the 10s (and I suspect but didn't check) back to the 07s or 06s, the owners manual is going to specify 88861800.

Ikester

I just had my 2000 MN6 rebuilt by ECS. I had switched to Amsoil ATF back in 2006 because back then the information on paper blocker rings were on 97-99 C5s. In 2009 my trans started to grind only at highRPM shifts. (4k RPM and up) On the track, it grinded on downshifts as well. There were even times when it grinded 4th gear at normal speed driving.

I then discovered this year that the paper blocker rings are on 2000 MN6s as well

ECS had advised me that my paper blocker rings were bad. I did not tell them I used synthetic fluid in there.

Oh well, lessoned learned; Knowledge is power! I now have a fully built MN6 and they put Amsoil back in which I wanted. I also swapped my rear diff fluid to Amsoil Severe Gear 75w-140 as I have 4.10s and track the car. 9i had Amsoil severe gear 75w-90 prior with no issues; just wanted to go thicker this time.)

Anyway, just wanted to share real world experience.