You're speaking of buoyancy and flotation.
It depends on the density of the particles in question. IF the particles are denser than the liquid, then they will sink. If the particles are less dense than the liquid, they should be more buoyant. In a less dense fluid, it should hold more low density particles until saturation.
It is the additive package that provides the suspension capabilities for particles greater than "solution" size. Larger and denser particles will, in the absense of turbulence, I.E., fall to the bottom of the sump in still (motionless) oil.
For the most part, the Detergent-Dispersant package will suspend the less dense particles that are surrounded by the DD micelle, such as sludge and small metallic particles.
I think the thicker oils show more wear because they don't flow as quickly on startup, and they don't cool as effectively as the thinner oils. Anytime you have thinner fluids, the flow rate will be slightly greater with the pressures being equal. The greater viscosity equals a greater pipe restriction, by analogy.
[ July 22, 2003, 02:13 PM: Message edited by: MolaKule ]