Originally Posted By: BearZDefect
NightRider, I am only writing my opinion based on my limited experience. My sample is too small to generalize very far.
Your Q45 is rear wheel drive, a different transmission entirely from those I am familiar with. It might work flawlessly with Dexron VI.
It isn't hard to find viscosity numbers for some ATFs. Generally, Dexron VI is about 6 cSt at 100*C and Mercon V is about 7.5-8cSt, which I think is similar to Dexron III.
I've seen claims that Dexron VI is shear stable, so it will stay near 6cSt for its service life. Maybe so, but in my case its viscosity went down by 5,000 miles of service, to the point that my transmission whined with it. Previously Dexron IIIh with well over 10,000 miles in service didn't cause any such symptoms in my transmission.
On a side note, the reason I'd choose Mercon V over Import MV for a matic-D transmission is these transmissions do not require HFM fluids. Where they are not required these HFM fluids make the shifts too soft (longer clutch engagement) for my liking.
Again in my limited experience, Dexron III, Dexron VI, and Mercon V aren't very far apart with the friction modifiers. Castrol Import MV is *very* different in the friction department. It works very nicely in newer transmissions that require such characteristics.
Thanks for your reply. I've been researching since my last post about visocity levels of Dex VI. Dex VI does remail at 6 cSt through out the life of the atf. Look at this GM link I found
http://www.sandyblogs.com/techlink/2009/05/dexron-vi.html After looking at this and many other sites, Dex III shears almost immediately, so it seems that the higher starting viscosity number doesn't matter.
Last question...is the new Mercon V shear stable like the Dex VI? Does it stay in the same viscosity range?