So, seems like reading in many places, a synthetic ATF is recommended for high mileage applications. At 213k, I figure that includes me.

Now, Mobil 1 has a synthetic that they say meets the Honda ATF-Z1 specs, and it's Dexron III (which isn't sold as that anymore.)

Now, I hear many say you can only use the Honda, but the Haynes Manual says you can use Dexron II.

So, what's the best ATF?

 

Consider that the honda shift valves are a steel plunger into the valve body bore, no 'O' rings, just a very close fit..... like .001"
So what do you think happens when cheapo trans fluid builds up varnishes on the plunger and bore?

Trust me, poor old Hondadude has spent hours and hours working valve plungers back and forth with solvent and Honda ATF to clean them up and get good smooth action restored.

The Honda Z-1 ATF has a claim to fame in the facts of having great cleaning properties as well as a very tiny molecule for lubrication.

To be honest, I've never opened up a trans that has been run 100k miles or more with synthetics.

 

Alright, thanks. I simply asked due to the fact that I get harsh shifts, and as far as I know, there's Honda ATF in there.

 

Honda transmissions of that era do shift under positive pressure, but if it is SLAM shifting there could be problems.
Also check to be sure the pressure lever cable is adjusted correctly.
A recent post involved that adjustment.
https://honda-tech.com/zerothread/2429398