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Russell Duffy wrote:
Message
Ah-h-h; something doesn’t compute here, at least
not for me. Did you start from the same temp? Was the air a lot
cooler? More air blowing through the cooler? More oil in the pan? A
slight reduction in viscosity can’t account for the difference. The
flow rate will be essentially the same, as I think your pressure drops
confirm; so-o-o-o what makes the heat rejection rate double?
Same
temp, same everything. The only diff was the oil viscosity. One of
the reasons I tried this was because Bruce T mentioned that thinner oil
would transfer heat better than thick oil. Do you disagree with that?
But it does bring up the question, what is the
recommended oil viscosity? 5W30 seems a bit low.
I'm not
sure what the RX-8 uses, but 5W30 is the standard weight in almost
every vehicle made now. Bruce's personal suggestion was 10w40, but
Mobile One doesn't come in that weight. As far as I've seen, the
choices for Super Syn are 5W30, 10w30, and 15w50.
Rusty
Please allow me a comment or two here.
What most people are interested in when they "go up in weight" in oil
is more bearing protection i.e. less possibility of metal crankshaft
(or eshaft) hitting metal bearing material under the most drastic of
circumstances, high speed, high stress operations. More weight = more
"cush".
What they are unaware of, for the most part, is that this function is
better increased by upping the "shear strength" of the oil, and indeed
the oil's weight has little or nothing to do with that figure in a
synthetic.
It is measured by putting a drop or two between two perfectly flat
plates that are squeezed together until the film breaks. Most
petroleum products fail at about 200-400 PSI. Most synthetics hold on
until 2000 - 3000 PSI, a level up in magnitude near TEN. See why
people who abuse their oils like synthetics?
Mobil 1 makes a ZERO weight oil that is "state of the art" ... It
almost takes a leap of faith to pour 0 weight oil into your engine ...
but if you look at the numbers, the shear strength is incredible. I
have no doubt that ZERO weight Mobil One far exceeds the film strength
of 90 Weight gear oil! ANY petroleum product, for that matter.
With ANY synthetic, every molecule is identical to every other molecule
(+ certain additives, but not significant). The strength of the
bonding is due to the fact that the atomic centers are very closely
packed and identical.
Think of plowing your hand into a barrel that contained ping pong
balls, a few baseballs, some marbles, some tennis balls, a few golf
balls, some buckshot, some BB's, and maybe throw in a softball or two
(like petroleum, with different sized molecular chains) . Ouch! but
your hand slides in through and around the spheres without too much
problem. Now fill the barrel with all BBs. You would break your
wrist with the same amount of force as before, and still not "shear the
bonds". That is a bit simplistic, but it is an easy to think of it.
(Inversely proportional to the square of the distance between the
atomic centers, if I recall correctly ... but don't hold me to that one)
Anyway ... don't think "weight" ... think "shear strength". Also, we
don't "hammer" our oils in a rotary anyway until RPMs start exceeding 9
grand. Minimum bearing resistance is at a "sweet spot" low ... near
5600 and near where we cruise if I recall correctly and have learned
anything from reading this list :-)
Dale Smith
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