What you're missing is that bulk viscosity has little to no relationship to
the lubricating performance in thin films at high contact pressures, and
that the spacings and tolerances are in the bearing are differant/smaller in
the newer engines so a lower visc is required/desired. The lower viscosity
oils do cause lower pumping losses and narrower visc ranges e.g. 5W-20 vs
5W-30 or 10W-30 vs 10W-40 or 10W-50 require less viscosity modifier
additives (which tend to break down over time). So in short, use what is
recommended, though it may seem odd at first.


"Vic Dura" wrote in message
...
I just bought a new car last month. My previous car was a 1997 model
and it specified 10w-40 motor oil, as had every car I have owned for
the past 30 years. This new car (a 2005 Ford Focus) specifies 5w-20
oil. I've since found out that 5w-20 has been pretty much standard for
the past couple of years.

Question: Why the apparent reduction in lubricating requirements? I
can understand that theoretically the 5w requires less power to pump
and therefor *might* result in some mileage improvement; but the high
temp reduction from 40 equivalent to 20 equivalent doesn't make sense
to me.

What am I missing?

--
To reply to me directly, remove the CLUTTER from my email address.