Return-Path: Received: from cardinal.mail.pas.earthlink.net ([207.217.121.226] verified) by logan.com (CommuniGate Pro SMTP 4.2.3) with ESMTP id 434705 for flyrotary@lancaironline.net; Mon, 27 Sep 2004 19:46:14 -0400 Received-SPF: pass receiver=logan.com; client-ip=207.217.121.226; envelope-from=timepilot@earthlink.net Received: from user-0c8gki1.cable.mindspring.com ([24.136.82.65] helo=earthlink.net) by cardinal.mail.pas.earthlink.net with esmtp (Exim 3.33 #1) id 1CC5Bf-0000GY-00 for flyrotary@lancaironline.net; Mon, 27 Sep 2004 16:45:43 -0700 Message-ID: <4158A60B.4040108@earthlink.net> Date: Mon, 27 Sep 2004 16:45:15 -0700 From: Dale Smith User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.4) Gecko/20030624 Netscape/7.1 (ax) X-Accept-Language: en-us, en MIME-Version: 1.0 To: Rotary motors in aircraft Subject: Re: [FlyRotary] Re: Oil viscosity References: In-Reply-To: Content-Type: multipart/alternative; boundary="------------010607080001020408020209" This is a multi-part message in MIME format. --------------010607080001020408020209 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Russell Duffy wrote: > 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 --------------010607080001020408020209 Content-Type: text/html; charset=us-ascii Content-Transfer-Encoding: 7bit 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
 --------------010607080001020408020209--