tjkj2002 wrote:
Quote:
They believe that viscosity is important in the process of lubrication, which is false.
It actually is(sort of),improper viscosity leads to inproper oil pressure,which leads to oil not getting to the right places or not enough oil getting to the right places.Inproper viscostity also reduces the "oil buffer" zone between the bearings and crankshaft which will toast your bearings after awhile,the same goes for the camshaft bearings,and hydrualic lifters.
Remember those older Castrol GTX oil comercials that showed the engine internals? That's what I'm talking about.
Most multi-viscosity engine oils contain special types of additives. In the context of synthetic oils, these oils do not rely as much on special Viscosity Index Improver additives simply because they experience little permanent viscosity loss. This is why the Amsoil 0W30 is such a great oil. Lubrication is built into the additive package and is primarily dependant on film strength. There is no required regulation concerning the levels of shear stability for engine oils, however, testing shows that lower percentages results with an oil that is more shear stable and will retain its viscosity much better during operation. Like tjkj2002 said, improper viscosity, especially in the use of multi-viscosity oils does play a role. As the oil passes through the engine, these molecules are permanently sheared or torn apart over time, causing the additive to lose its viscosity-contributing advantages, which reduces the oils ability to maintain its higher number. Oil goes through a lot of abuse and will reach extreme heat and extreme friction in the oil pump, cam shaft, and piston rings. Since viscosity varies inversely with temperature, its value is meaningless unless accompanied by the temperature at which it is determined. With petroleum oils, viscosity is now commonly reported in centistokes. A thin oil has a lower number and flows more easily, while thick oils have a higher number and are more resistant to flow. The standard unit used to measure viscosity is the centistokes. The centistoke rating is converted into the SAE weight designation. Multi-weight or multi-viscosity oils (for example: 5W-30) are made by adding polymers to oil. The polymers allow the oil to have different weights at different temperatures. The first number indicates the viscosity of the oil at a cold temperature, while the second number indicates the viscosity at operating temperature. For example: At cold temperatures, the polymers are coiled up and allow the oil to flow as their low numbers indicate. As the oil warms up, the polymers begin to unwind into long chains that prevent the oil from thinning as much as it normally would. The result is that at 100 degrees C, the oil has thinned only as much as the higher viscosity number indicates. Another way of looking at multi-viscosity oils is to think of a 5W-30 as a 5 weight oil that will not thin more than a 30 weight would when hot.
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