Jim....
Don't kid yourself, my friend. You should
get more oil pressure with the heavier oil
but you should be getting a minimum of
55-60 hot with the 10W-30 as well, most
especially if you are running an oil cooler.
Going back to the 20W-50 treated the
symptom, not the cause, which could
be something as simple as removing
the oil pressure reliefe valve and spring
and cleaning up the "seat" while renewing
the valve and spring.
And I think this may be the problem
because the 20-25lbs idling you got when
"hot" with the thinner oil indicates that
both oil pump and bearing clearances are
good........
so methinks the reliefe valve is the
culprit with respect to lower than normal
oil pressures at the "top" at speed when
"hot", using the thinner 10W-30.
Assuming you are not using synthetic,
initial flowability of 20W-50 at 30F+-
is less by far than 10W-30. It is estimated
by many of those that know that 50% of
engine wear occurs during cold starts for
this very reason (this is one of the ways synthetics outperform mineral
oils in
addition to film strength).
Fix "the problem" and your 10W-30
will work just fine in winter weather
and save you engine wear which translates directly into $$$$$$$ over
use and time!!!
I AM on your side, fellow lister!! :):)
Cap'n. Bob
'60 :{)
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