I drive a honda 2005 V6- very cool ride that E. A Bimbo (Inspired) got for me.
I got interested in transmissions and transmission oils when the driver bringing it down almost gave me a heart attack by putting ABRO in the gearbox. PUSHKA!
Thankfully, it was resolved before any damage was done.
But it has got me interested,

Chemical engineers, in their bid to improve the trans oils available to cater to the newer, sophisticated gearboxes been developed (and make plentyyy money in the process) have compounded new oils left, right and center.

Now, we all know that Honda's are not particularly noted for building excellent transmissions, so if you have a honda you may need to pay attention and be quite deliberate in the maintenance of its transmission.

So enough about the generalizations, my immediate discussion concerns dexron III (and related oils) and Honda ATF-Z1. Honda recommends the exclusive use of Honda ATF-Z1, but says that if not available, a dexron III oil should be used as a temporary stop gap until it can be replaced with the Honda ATF-Z1.

From my research, it would seem that Honda ATF-Z1 is a moderate base oil, a little less viscous than oils branded dexron III (the classification has been discontinued but remains popular). It is modified with the additive called Z1 which is supposed to modify the features of the fluid without affecting its ability to effectively lubricate the transmission. From what I've read however, the general consensus it would seem is this; Z1 affects the viscosity of the fluid by actually reducing it.

The reason for the Z1 additive is to lower the frictional coefficient of the liquid enabling the clutch plates slide over each other at lower engine revolutions/speeds enabling the "imperceptible" shift. What this means is, when driving, a driver will hardly notice the transmission shifts up or down. I see that the opinions is, smoother shifts sell cars but work the gearbox hard and wear it out faster.

Other conventional dexron III liquids make the gearbox operate more "conventionally": the clutch plates don't slide over each other until a certain specific frictional coefficient is reached. The trans shifts are firmer and feel like the those of the first generation auto shifts. But the fluid holds the gearbox parts more "firmly" and prevents them from sliding at the slightest provocation. Which in essence keeps the gearbox longer and in better shape.

So my thinking is, a "firmer" feel on my gearbox is a small price to pay if dexron III maintains it better especially since its older. I saw an article where the author who claimed to have worked for honda helping them develop and test gearboxes said that in a field test with dexron III, the hondas 2004 and 2005 had been able to tow a vehicle each of similar size and shape without wahala even uphill, but that with ATF-Z1, they were unable to do any major pulling.

I'm running coastal dexmerc in my transmission. (It costs just a little less than the Honda ATF-Z1 which is not even available commercially.) I've run it for 2 months, and the liquid looks, feels and smells the exact same way as the day it was put in.

Only thing is that after running for a while, the gear shifts become a bit harsher. I did some research and this is attributed to the torque converter in the gearbox "locking up" because the fluid is heavier and thicker than the Z1. In a couple of articles I read, the authors were so bitter at Z1- and vowed not to ever allow a drop in his hondas. The torque "lockup" was a small price to pay and a number of them were investigating their own additives to reduced "lockup" which I see is described as a "harmless nuisance to smooth shifting".

Experts in the house- can I get some opinions on the issue? Wordd.