<VV> Oil Specs

[James Davis]

Anyone with a digital oil pressure gauge, using synthetic oil, can easily 
verify that, indeed, the oil's viscosity index decreases (oil gets thicker) 
as the oil cycles over its heat range.
Jim Davis


At 04:56 PM 7/1/2005, BobHelt at aol.com wrote:
>In a message dated 6/29/05 11:53:11 AM US Mountain Standard Time,
>HallGrenn at aol.com writes:
>
> > Bob,  Everything I have read says the multigrades can't meet the viscosity
> > requirements at operating temps at the end of their life.  I know the API
> > viscosity limit is there as a STANDARD for oils, but I don't know of any
> > evidence
> > that any of them get thicker or increase in viscosity as they wear.
>
>Bob,
>API  spec IIIG requires that all oils sold with the donut on the back of the
>container, or the starburst on the front of the container, meet the viscosity
>requirements of no more viscosity INCREASE than 150% during a 100 hour full
>power test with the oil at 150 degrees C (304 deg F).  Spec IIIGA requires 
>that
>the viscosity be checked every 10 hours during this 100 hour test and that 
>the
>oil be compared to that of the new original oil, with both samples at 40 deg
>C. Note that a 100 hour test is the equivalent of 5000 miles at 50 mph. So 
>the
>API is definitely concerned about viscosity increases of the oil during use,
>not viscosity decreases. If the API wen't concerned with viscosity increase,
>they wouldn't have included this into their spec. All GF-4 and SM oils MUST
>meet this spec.
>
>It is true that the SAE requires that a minimum viscosity of an oil at 150
>deg C be met, but other than the thinning at the elevated temp, there is no
>implication that the oil loses viscosity during use or that the viscosity 
>fails to
>meet spec during use.
>
>Thus we can know that it's not viscosity decreases we need to be concerned
>with, but viscosity increases during use.
>
>Regards,
>Bob Helt
>  _______________________________________________
>This message was sent by the VirtualVairs mailing list, all copyrights are 
>the property
>of the writer, please attribute properly. For help, mailto:vv-help at corvair.org
>This list sponsored by the Corvair Society of America, http://www.corvair.org/
>Post messages to: VirtualVairs at corvair.org
>Change your options: http://www.vv.corvair.org/mailman/options/virtualvairs
>  _______________________________________________