[ncmncm]

Cold oil lubricates better.

It has higher viscosity, meaning it takes more energy to move it out of the way. As it warms up, its lubricating power decreases, but not too much, and its viscosity decreases, enabling better engine efficency. A cold engine is less efficient, but only for a short time, until it heats up.

Oil too thick to pump rarely happens in normal life. In arctic and subarctic conditions people use electric heaters to keep the oil thin enough to pump.

[chrisseaton]

> Cold oil lubricates better.

By this logic a solid would be the best lubrication, which it clearly isn’t.

[ncmncm]

If you had solid oil -- i.e., wax -- between your moving parts, metal would not be touching metal, so no wear, but the force needed to move the parts would be large. With cold but not solid oil, the effect is similar, but less.