"TeGGeR®" <tegger@tegger.c0m> wrote
E
> > If Honda thought 10W-30 or -40 today is dangerous to the
> > transmission, I think they would have said something.
>
> They have.

Sort of. But I don't discount the substance of what you
cited.

> An example from the '02 RS-X manual (pg 13-4):
> "Always use Honda Manual Transmission Fluid (MTF). Using
motor oil can
> cause stiffer shifting because it does not contain the
correct additives."

ISTM a manual transmission is pretty much a manual
transmission, so I agree that what's written in the 2002
Honda manual you cite above should apply to any year's
transmission, including my 1991 Civic's. In the future, I
will take note of it in posts, as it is helpful.

OTOH, I remain hesitant to translate this to a prediction of
disaster if one uses 10W-30 or -40. I can see that "stiffer
shifting" implies more wear, but ISTM it might be
negligible. Especially since the statement is qualified with
"can cause" vs. "will cause." To read this like a lawyer
blah blah...

So I'm not panicked on this point. My intent, stated in the
recent past, is to switch my 91 Civic to Honda MTF when the
next tranny oil change is required, see if the shifting is
superior, and draw more conclusions then.