Originally Posted by oilman
So for example a petroleum based 10w-60 which is a wide viscosity oil (0w-30 is a narrow viscosity oil) requires a lot of VI Improvers to make it work, by this I mean that these special polymers are added to make a 10 base oil a 60 when hot.
Here's where the problem occurs, these polymers are prone to shearing with heat and therefore they cause the oil to lose viscosity - With me so far?
So, a 10w-60 will most likely be a 10w-40 within a few thousand miles and losing viscosity all the time giving less protection than a good 10w-50 synthetic oil.
I don't understand now. You're trying to say that top of the line high ciscosity oil will degrade faster then middle shelf normal oil? We're not talking about petroleum ased mineral oil but top motorsport stuff here. I mean everybody here changes oile very often - so no need for longlife oils. You say 10W60 will perform like 10W40 after some time. But 10W60 will degrade faster, won't it? So which one will be better protection after lets say 1k miles 2k miles up to 5k miles? When usually people here change oil. And you forget about such factors as amount of oil in the engine which has some impact on it's lifetime.
Once again I'm only tring to understand you point better. Hope that isn't a problem.
It's quite important thing as you are speaking agains basically any tuner, motorsport service, performance car centre I know....