SUS & cSt viscosity. Why the difference?

[SJohnson]

So here's what I don't understand. I recently did a UOA. Oil was regular MaxLife 20W-50. The oil was used in my Harley. Everything looked good except the SUS & cSt were slightly out of spec. SUS was 81.6, S/B 82-95. cSt was 15.93, S/B 16.0-19.4. So both were barely out of grade on the low side. Here's the report:

http://www.bobistheoilguy.com/forums/ubb...248#Post3629266

So, I started looking around at other 20W-50 UOA's and VOA's and noticed the SUS & cSt ranges were different depending on the manufacturer. Here's one for VR-1 and another for Syn 3 that shows a SUS range of 77-94 and a cSt of 14.8-19.2.

http://www.bobistheoilguy.com/forums/ubb..._HD#Post1967684

http://www.bobistheoilguy.com/forums/ubb..._49#Post3662849

Here's one for VOA of the same Syn 3 oil that shows SUS of 81-102 and cSt of 15.8-21.1.

http://www.bobistheoilguy.com/forums/ubb...gle#Post3652062

And finally, here's some Redline that shows SUS of 86-102 and cSt of 17.0-21.1.

http://www.bobistheoilguy.com/forums/ubb...n_a#Post3394549

So why are the SUS and cSt different for the same "weight" oils? Why are the Syn 3 VOA and UOA different? How much of a concern is it that the MaxLife was slightly lower that it should be? If it was Syn 3 or VR-1, it would still be in spec. I've done a lot of searching and I can't find the answer and it doesn't make sense to me. I'm sure someone here knows the answer and can explain it to me.

Thanks in advance.

 

[MolaKule]

Look at the Grade charts for SAE 50 grade engine oils,

http://www.bobistheoilguy.com/viscosity-charts/

and for a 50 Grade you will see the Kinematic viscosity @100C can range from about 16.5 cSt to 21.5 cSt.