This is a funny area of science, this is
what I know off the top of my head, no
internet reasearch or study to backup
the statements.
1. Engine bearing tollerances are 1-2
thousands of an inch, 1.5 is about right,
and this has not changed much, as far as
I know in recent years.
2. Oil has a "measurment" and a micrometer
can measure this thickness, it's in the range
of .75-1 thousands of an inch, as far as I
know, this measurment is the same for 5-30
or straight 40 weight oil. The weight of the
oil determins how thin "vescosity" when hot,
like the difference in pumping gear oil into a
diff and pumping motor oil into an engine, yes
I know they are not hot, yet, but the effort required
is substantially greater to pump gear oil.
Hot or cold a thicker oil will take more power to pump.
3. Oil needs room to flow, and a tight tollerence
reduces the oils flow rate, less oil means heat, most
people don't realize that oil plays a major roll in
cooling, as well as lubricating, cleaning, protecting
from rust, corrosion of acids, carbon suspension (black
oil is full of carbon) and wear reduction, motor oil is
the most reasearched fluid on planet Earth, bar none.
In a press conference years ago, some VW engineers
were asked about the unusually high oil temps in their
engines, and after a few moments to convert the Degrees
F* to Degrees C* their reply was that the oil temp was fine,
and if it was lower they would not get the fuel mileage that
they were supposed to get, so now go out and look at the
bottle of 5-30 and read the front, I think it will say Fuel Saving
or some other similar statement like Saves Gas ..........
I welcome anyone to reasearch and throughly dive
into this subject, we might even all learn somthing
and come away with a greater knowedge on the matter.
BTW I use 5-30 in winter, 10-40 in the warm months,
and 20-50 in the hot summer, and I do this for the flow
and cranking speed that I want to have in these types
of weather temps
Wild