What role does viscosity play in a motor oil?
Engineers work to establish an optimal viscosity for an oil, based on load and speed conditions. They balance lighter – or low-viscosity – oil, which provides little resistance to motion thereby saving fuel and efficiently transferring horsepower, with a heavier – or high-viscosity – oil that resists being squeezed out of the contact area between metal surfaces. The complicating factor is that the viscosity of an oil varies with changes in temperature – thinner when hot, thicker when cold. At low temperatures, we need the motor oil to flow readily (not thicken too much or gel). At high temperatures, we need the motor oil to keep from becoming too thin and allowing metal-to-metal contact. Therefore, engineers developed multigrade motor oils.
