Ok so we all know that when PQIA tested 5w20 conventional oils, the PYB & QSGB stood out with very low NOACK & a very good low temp -30C viscosity which can only be explained by the use of Group III base stocks.
http://www.pqiamerica.com/Feb2014/consolidated5w20ALL.html
The most popular theory is that Shell had an over supply of GTL base stocks & maybe some lucky batches were made with it instead of a regular Group II base.
I have a different theory. I believe that it wasn't just a few lucky batches, but maybe up to 50% of all PYB & QSGB are made with a Group III+ base.
My reasoning:
-Group III+ base stocks have a VI of at least 140 which is very close to the 155 VI of the oils tested
-Regular Group II base has a VI of 80-119 which means a lot of VI improvers must be added to reach 155 VI
-More pour point depressants must be used with regular Group II to get the low temp performance up to spec
It might be cost effective to just use a Group III+ base stock in PYB & QSGB which doesn't require the use of VI improvers for "dino spec" oils of only ~155 VI. Also, not requiring as much pour point depressants to achieve low temp specs is another cost saver.
On paper it looks like the only differences between PYB & PP is that PP has more VI improvers in it which also increases NOACK from 6.5% to ~10%, and maybe a higher TBN to support longer drain intervals.
http://www.pqiamerica.com/Feb2014/consolidated5w20ALL.html
The most popular theory is that Shell had an over supply of GTL base stocks & maybe some lucky batches were made with it instead of a regular Group II base.
I have a different theory. I believe that it wasn't just a few lucky batches, but maybe up to 50% of all PYB & QSGB are made with a Group III+ base.
My reasoning:
-Group III+ base stocks have a VI of at least 140 which is very close to the 155 VI of the oils tested
-Regular Group II base has a VI of 80-119 which means a lot of VI improvers must be added to reach 155 VI
-More pour point depressants must be used with regular Group II to get the low temp performance up to spec
It might be cost effective to just use a Group III+ base stock in PYB & QSGB which doesn't require the use of VI improvers for "dino spec" oils of only ~155 VI. Also, not requiring as much pour point depressants to achieve low temp specs is another cost saver.
On paper it looks like the only differences between PYB & PP is that PP has more VI improvers in it which also increases NOACK from 6.5% to ~10%, and maybe a higher TBN to support longer drain intervals.