Return-Path: Received: from fed1rmmtao02.cox.net ([68.230.241.37] verified) by logan.com (CommuniGate Pro SMTP 4.2.3) with ESMTP id 435540 for flyrotary@lancaironline.net; Tue, 28 Sep 2004 14:02:50 -0400 Received-SPF: none receiver=logan.com; client-ip=68.230.241.37; envelope-from=ALVentures@cox.net Received: from BigAl ([68.107.116.221]) by fed1rmmtao02.cox.net (InterMail vM.6.01.03.04 201-2131-111-106-20040729) with ESMTP id <20040928180218.CCMC21420.fed1rmmtao02.cox.net@BigAl> for ; Tue, 28 Sep 2004 14:02:18 -0400 From: "Al Gietzen" To: "'Rotary motors in aircraft'" Subject: RE: [FlyRotary] Re: Oil viscosity Date: Tue, 28 Sep 2004 11:02:17 -0700 Message-ID: <000001c4a585$4b770060$6400a8c0@BigAl> MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----=_NextPart_000_0001_01C4A54A.9F182860" X-Priority: 3 (Normal) X-MSMail-Priority: Normal X-Mailer: Microsoft Outlook, Build 10.0.6626 Importance: Normal In-Reply-To: X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2900.2180 This is a multi-part message in MIME format. ------=_NextPart_000_0001_01C4A54A.9F182860 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable I don't want to over-work this issue, but I would like to suggest some caution (and/or some research on oil properties) before rushing off to = solve a cooling system problem by changing the oil viscosity grade. The = choice of oil should be made by the service requirements of the engine. Certainly = oil properties are not a simple subject and it would take a book to cover = all the factors. At the least I would think that Mazda's recommendation for = the engine, for moderate to severe service, should be followed. =20 Viscosity grade is only one of a dozen or more measures of oil = performance, and is a measure of how easily it flows, at specific temperatures. The = dual numbers on a multi-grade refer to its viscosity behavior at a low temp (can't remember if it is 0F or 0C), and at a high temp (100C, 212F). A 5/30, 10/30 and 15/30 all have the same viscosity at 100C, so at our operating temperature they are all very similar. But the wider the viscosity grade range results in some compromises, especially in = petroleum oils, where long chain polymers are added to extend the range from the = base grade. =20 Among the other measures of oil performance are film strength (high temperature shear), viscosity index, surface adhesion, flash point, = flame point, dispersant ability, ash content, CCS rating, additives, = resistance to temperature breakdown etc, etc. One of the most important of these = measures in determining the protection against engine wear is the film strength. Film strength is directly related to viscosity because the longer chain molecules that result in higher viscosity also result in higher film strength. In petroleum oils, single grade invariably has higher film strength than a multi-grade with the same high temp viscosity, = especially after they have run for awhile. =20 Premium synthetics have generally much better film strength, and most = other qualities, than petroleum oils. For our service in an airplane, which I would rate as moderate to severe, I would not want to use petroleum oil = with a high temp viscosity (the high number on a multi-grade) of less than 40 = to 50, and would probably opt for a 20/50 in a quality multi-grade. You = can go to a lower high temp viscosity rating in synthetic, so maybe 30 to 40 = for the high number on the multi-grade. And synthetics can be formulated in multi-grade without adding polymers, so a low range isn't as important, = but the greater the range, the more of a compromise. Unless you live in a = cold climate where you may have frequent starts in below freezing conditions; = a 10/30 or 15/30 would likely be a better choice than a 5/30. If I'm = running a racing engine (severe service) I might want 20/50 even in a synthetic. =20 Choice of viscosity also depends on porting in the engine, bearing clearances, etc. The manufacturer's recommendation is a good staring = point. I personally do not know what Mazda's recommendation is for the rotary = in moderate to severe service. You would generally not want to go more = than one grade higher than the recommended for a stock engine. =20 I've drawn some of my own conclusions, but everybody has their own. A pretty good, but somewhat wordy reference is The Motor Oil Bible that = you can download free at www.themotoroilsite.com . His rankings for the best in a 10/30 would be Redline, Amsoil, and Neo; = in a 10/40 would be Amsoil, Redline, Mobil-1; in a 15/40 Redline, Neo and = Amsoil. But I would guess any of his top five ratings in any grade would be excellent choices. =20 Just scratching the surface, FWIW. =20 Al ------=_NextPart_000_0001_01C4A54A.9F182860 Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Message

I don’t want to over-work = this issue, but I would like to suggest some caution (and/or some research on = oil properties) before rushing off to solve a cooling system problem by = changing the oil viscosity grade.  The choice of oil should be made by the = service requirements of the engine.  Certainly oil properties are not a = simple subject and it would take a book to cover all the factors.  At the = least I would think that Mazda’s recommendation for the engine, for = moderate to severe service, should be followed.

 

Viscosity grade is only one of a = dozen or more measures of oil performance, and is a measure of how easily it = flows, at specific temperatures.  The dual numbers on a multi-grade refer = to its viscosity behavior at a low temp (can’t remember if it is 0F or = 0C), and at a high temp (100C, 212F).  A 5/30, 10/30 and 15/30 all have the = same viscosity at 100C, so at our operating temperature they are all very = similar.  But the wider the viscosity grade range results in some compromises, = especially in petroleum oils, where long chain polymers are added to extend the range = from the base grade.

 

Among the other measures of oil performance are film strength (high temperature shear), viscosity index, surface adhesion, flash point, flame point, dispersant ability, ash = content, CCS rating, additives, resistance to temperature breakdown etc, = etc.  One of the most important of these measures in determining the protection = against engine wear is the film strength.  Film strength is directly = related to viscosity because the longer chain molecules that result in higher = viscosity also result in higher film strength.  In petroleum oils, single grade invariably has higher film strength than a multi-grade with the same = high temp viscosity, especially after they have run for awhile.

 

Premium synthetics have generally = much better film strength, and most other qualities, than petroleum = oils.  For our service in an airplane, which I would rate as moderate to severe, I = would not want to use petroleum oil with a high temp viscosity (the high = number on a multi-grade) of less than 40 to 50, and would probably opt for a 20/50 = in a quality multi-grade.  You can go to a lower high temp viscosity = rating in synthetic, so maybe 30 to 40 for the high number on the = multi-grade.  And synthetics can be formulated in multi-grade without adding polymers, so = a low range isn’t as important, but the greater the range, the more of a = compromise.  Unless you live in a cold climate where you may have frequent = starts in below freezing conditions; a 10/30 or 15/30 would likely be a better = choice than a 5/30.  If I’m running a racing engine (severe service) = I might want 20/50 even in a synthetic.

 

Choice of viscosity also depends = on porting in the engine, bearing clearances, etc. The manufacturer’s = recommendation is a good staring point.  I personally do not know what = Mazda’s recommendation is for the rotary in moderate to severe service.  You would = generally not want to go more than one grade higher than the recommended for a stock = engine.

 

I’ve drawn some of my own conclusions, but everybody has their own.  A pretty good, but = somewhat wordy reference is The Motor Oil = Bible that you can download free at www.themotoroilsite.com.

His rankings for the best in a = 10/30 would be Redline, Amsoil, and Neo; in a 10/40 would be Amsoil, Redline, = Mobil-1; in a 15/40 Redline, Neo and Amsoil.  But I would guess any of his = top five ratings in any grade would be excellent choices.

 

Just scratching the surface, = FWIW.

 

Al

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