In any case, today's Castrol smells nothing like Castrol from the '60s and
'70s. It must be an entirely different formulation.

I figured it must be different now too, but that old memory has kept me away
from Castrol ever since. Those guys too, had the drop in pressure with the
castrol. Mine was much less with the Kendall (later GT-1).

We wound up using a heavy-duty Wolf's Head that's no longer available, BTW.
It really held pressure well when it got hot, without being excessively
thick when it was cold.

Ed Huntress
I always heard good things about WH oils but they were hard to find down here
in FL back then.
Greg Sefton