Originally Posted By: insomniac
This is elementary, I know.
Oil thickens as it cools and thins-out as it gets warm/heated up, correct? Someone just told me "No", multi-grade oils are designed to behave the opposite because of the VIs in them.
Comments?
The VII's keep a multi grade oil from thinning "as much" when it gets hot. They dont make oil get thicker when hot.
10w40 = SAE10 when cold and SAE40 when hot.
SAE10 when cold is thicker than SAE40 when hot.
In simple terms, as heat builds, the VII's expand thus slowing the thinning process to make the SAE10 act like a SAE40, but it still thins out, just not as much as a SAE10 would.
When the engine is turned off, the oil eventually cools, and the VII's retract, thus keeping the oil from thickening "as much" as a SAE40 would otherwise, but it still thickens as it cools.