Originally Posted by MolaKule
There are three (3) key features of polymer viscosity modifiers, specifically VII VM's:
VII and VM are the same thing.
Originally Posted by MolaKule
They do modify the rate of change in viscosity verses temperature.
No, this is the most common misconception about VIIs. They do not modify the rate of change of the viscosity vs. the temperature.
Most VIIs boost the viscosity by roughly the same factor at all temperatures. (PMA is an exception but it's not commonly used in motor oil.)
The way the viscosity index VI is defined is such that even if you multiply KV40 and KV100 by the same number (which is what a typical VII does), VI increases. Hence, it's called a VII. They do not selectively boost the viscosity at high temperatures as most people incorrectly believe. This is why there is no difference between a VM and a VII.
The advantage of using a VII comes at cold cranking. Cold-cranking simulator (CCS) is a high-shear test and the VII shears and the oil passes the test by measuring below the maximum CCS viscosity limit.
There are three (3) key features of polymer viscosity modifiers, specifically VII VM's:
VII and VM are the same thing.
Originally Posted by MolaKule
They do modify the rate of change in viscosity verses temperature.
No, this is the most common misconception about VIIs. They do not modify the rate of change of the viscosity vs. the temperature.
Most VIIs boost the viscosity by roughly the same factor at all temperatures. (PMA is an exception but it's not commonly used in motor oil.)
The way the viscosity index VI is defined is such that even if you multiply KV40 and KV100 by the same number (which is what a typical VII does), VI increases. Hence, it's called a VII. They do not selectively boost the viscosity at high temperatures as most people incorrectly believe. This is why there is no difference between a VM and a VII.
The advantage of using a VII comes at cold cranking. Cold-cranking simulator (CCS) is a high-shear test and the VII shears and the oil passes the test by measuring below the maximum CCS viscosity limit.