Originally Posted by OilUzer
Originally Posted by MolaKule
Originally Posted by OilUzer
I was under impression that too much vm is bad and it shears or burns or makes sludge or something ...
Sounds like they are as bad as I thought !?
Why would a formulator put too much VII in a formulation?
You only insert as much VII as is necessary to achieve your viscosity target.
If you can't achieve a viscosity target using the prescribed amount of VII then you need to change the viscosities of the base oil mix to get there.
Thanks for your reply.
I didn't word it correctly. By too much vm I meant if the gap is wider like in case of 5Wx30 vs. 10Wx30 ... 5Wx30 must use more vm compared to 10Wx30 and that's not desirable (i.e. relatively "too much vm") and IF you can live with 10W cold temp rating, best is to use lower vii oil ...
However after your reply, I recalled that SonOfJoe also saying that VMs aren't bad or as bad as people think or something to that effect.
I believe Solarent made that statement:
Viscosity Improvers are not bad
Anyway, after re-reading your original post I think I may see what you were pointing to.
VII's in engine oils are, in chem-speak, polymers. And polymers are subject to degradation and oxidation as any other additive component. The rate of degradation is highly dependent on molecular weight and the polymer's molecular structure, and engine condition and operation.
Another reason for not using any more VII than necessary is the cost, since VII's are more expensive than base oils, so it is desirable to use as little VII as possible to achieve the 100C kinematic viscosity.