Originally Posted By: A_Harman
I'm not fundamentally opposed to thinner oils. But I think the pursuit of "thin" has gone too far when the engineers are depending on the formation of tribological films on the bearings to prevent wear because the oil film thickness is too small to prevent metal-metal contact. If I were chief engineer of Engine X, I would decree that the bearings operate in full hydrodynamic lubrication up to 150C on the normal recommended oil. Then the tribo films could be depended on to give protection during marginal lubrication conditions. This is how robust systems are engineered.
Ahhh, how refreshing to hear proper design concepts in this day when (to quote them), manufacturers are spending more time in mixed/boundary lube regimes, for "normal" operation...simply, thy are removing the customer's head room. Not creating the pile of failed engines, as some would posit.
Originally Posted By: A_Harman
It seems that if engines are being redesigned with larger bearing areas and lower clearances, that would be increasing engine friction. But assuming that the auto manufacturers already know that, maybe they are reducing the parasitic drag of the oil pump enough to more than offset that.
Haven't done the math (it's a big afternoon), but you are correct. Increasing bearing surface area and reducing radial clearances to provide film thickness IS increasing drag...in the bearings....I don't think it's zero sum...might play that math over the holidays if I get really bored.
They may be making up for it in piston friction or somewhere else. Oil pump drag is pretty low, and probably better managed with variable displacement not viscosity.
