dexron III versus IV for modern PCM transmissions?

[jmo]

Hey Guys,

So in swapping out the trans fluid on my 2006 196 with the excal 330 motor and pcm transmission, the manual says to use dexron III, which I can't find as it was apparently decommissioned in 2006 in favor of IV. The only oil I see at the store which is labelled as fully compatible with III is Castrol dexron IV synthetic. Of interest the 2012 PCM owners manual still says to use dexron III, I would like to know if thats because they don't want to spend the time and effort to update their documentation and certify IV, or is there a specific reason why they want III over IV?

In searching for facts about why one would use III versus IV, this is the only fact based analysis I can find:

http://www.archivedsites.com/techlink/2009/05/

Given the excalibur is a GM motor, I assume the PCM transmission is also a GM product (yes I know what happens if you assume) shouldn't it follow GM's mandate that all transmissions that used to use III now must use IV?

Thanks,

JMO

[s_kelley2000]

Somebody please correct me if I am wrong but I am pretty sure that dex merc is as close as you can get to dex III and that it is what you should use. I believe dex IV is thinner and used in cars to give slightly better mpgs but I think you want something thicker for a boat trans.

[jmo]

Of interest I now see on Castrol's website that their Dex/Merc product is for dexron III applications,but it doesn't say that on the label on the bottle, maybe I will pull out the dex IV I put in and use the Castrol Dex/Merc.

[DanielC]

I have a 1997 Ski Nautique, with 2444.9 hours. My transmission called for Dexron 2. When I could no longer find 2, I went to 3, then 4, and currently I use Valvoline Dexron/Mercon ATF.

I am on a show ski club, so sometimes the boat pulls more than the recommended two skiers. Sometimes I pull a single girl on a swivel ski. Sometimes I pull a dock or a jump from a launch ramp to the show site.

My transmission fluid comes out looking new at 100 hours.

[jmo]

I have a 1997 Ski Nautique, with 2444.9 hours. My transmission called for Dexron 2. When I could no longer find 2, I went to 3, then 4, and currently I use Valvoline Dexron/mercon

Thanks Daniel, how long did you use dexron IV? I assume that's what your currently running?

[AirTool]

Somebody please correct me if I am wrong but I am pretty sure that dex merc is as close as you can get to dex III and that it is what you should use.

Yes....Dex/Merc is Dex 3. I would not use Dex 4 without a discussion with PCM and a good understanding of the difference.

I still find Mobil Dex/Merc at "some" of the corner Exxon Tiger Marts. (Mobil is now owned by ExxonMobil.)

Of course there are many other brands available. But, in the past, Mobil was always the best (tests showed) and the one recommended in the PCM manual.

[DanielC]

"Thanks Daniel, how long did you use dexron IV? I assume that's what your currently running? "

I did not run the IV very long. it seemed to switch to the dexron/mercon formula pretty soon after the IV was introduced. I am runing the dex/merc stuff currently.

[jmo]

What's interesting to me is the graph on the link I included above that illustrates the viscosity of Dexron IV over time remains constant, where as Dexron III starts off with a higher viscosity, but quickly drops and levels out with a lower viscosity than Dexron IV. The thing I am trying to figure out is what is the definition of "Test cycle" from an ASME standards point of view as it might be we are changing out the fluid well before it ever reaches the place on the graphs where the divergence happens, but based on the test data in the article it would suggest IV is better that III?

[scottb7]

http://www.mobiloil.com/USA-English/...uirements.aspx

http://www.mobiloil.com/USA-English/...exron_III.aspx

http://www.mobiloil.com/USA-English/...ion_Fluid.aspx

Question:

Does Mobil™ Dexron-VI ATF Meet Dexron III Requirements?

My 2000 Toyota Solara requires Dexron 3. Does your Dexron VI meet that requirement? I find the information on your transmission fluid bottles very difficult to understand; you should maybe look into making it a little user friendly.

-- Christian Easton, Markham, AR

Answer:

Dexron specifications are General Motors specifications. GM recommends using Dexron VI in all applications where Dexron III was originally recommended. Consider Mobil 1™ Synthetic ATF, which meets or exceeds the Dexron III requirements.

[Quinner]

Not sure if your post is suggesting too based on the answer, but Do Not Use Synthetic fluids in your trans.

[scottb7]

And the reason not too, even though gm is ok with it per mobile 1? ps...has anyone actually asked pcm?

[jmo]

And the reason not too, even though gm is ok with it per mobile 1? ps...has anyone actually asked pcm?

I lobbed the question into PCM this morning, I will report back on what they say.

[scottb7]

thanks much. i am 1 for 2 for them responding.

[shag]

My experience with PCM and any synthetics, is that they (PCM) stop short of recommending it because in their eyes, people tend to increase the service intervals while using synthetic, which is something I do not think they are willing to endorse. My .02

[j2nh]

No synthetics in the tranny. The synthetic transmission fluid is actually too "slippery" and the transmission will slip.
Different story when it comes to motor oil. PCM does not allow for extended service if synthetic is used.