Pete C. wrote:

Another possibility is that the machine sat unused for a fair amount of
time and the grease in the bearings hardened. The grease should
reliquify ok, but certainly he should keep an eye on spindle temp for a
while.

I really don't trust ancient, hardened grease that may have contaminants
in it in a set of expensive spindle bearings.
I have experienced this "hardened grease" and I don't think it actually
does ever liquify after that process happens.
This machine could very well have the original 30 year-old grease in it!

Yes, Iggy should DEFINITELY watch the temp until he is satisfied that it
does level off. I have a feeling with an
~30 F rise in only 16 minutes, that the limit temperature is going to be
way up there. Now, that may be normal for
the sealed bearing Ser-II head, but it will cause spindle growth that
will be several thousandths of an inch. Especially because the ballnut
is all the way at the top end of the quill in the BOSS head, a full FOOT
above the spindle nose, the expansion can be considerable.
Now, assuming the limit temp rise is 60 F (twice as hot as it got in
only 16 minutes) and assuming the whole quill heated evenly (not
possible) then it would expand .005". Assuming the quill had a linear
drop in temp along the whole foot, the expansion would be .002". While
not hideous, that could mess up precision work.

Jon