A question that I have been afraid to ask about oil viscosity and flow rate.

“ the lower the temperature the greater the flow rate as it is less viscous.”

You sure about that?

 

The OP's point is that, at low temperature, modern multi-weight oils still flow pretty well (i.e., a multi-weight oil is less viscous at low temperature than a straight-weight oil with the same hot rating)..

This -- you want to get as much of the super-fine debris suspended up into the oil itself (and even a multi-weight oil is much less viscous when warm).

 

I’m no oil expert. The wikipedia article on oil, https://en.wikipedia.org/wiki/Motor_oil , says in part “The viscosity of a multi-grade oil still varies logarithmically with temperature, but the slope representing the change is lessened.”. I believe “varies” here really means “...decreases with increasing....”. The confusion probably arises from the thought that the two numbers in, say, 20W-50, represent absolute viscosities independent of temperature when in fact they refer to tests for viscosity taken at different temperatures.

 

as long as the oil is still warm the single particles in the oil are ntio setting to the grouns and when you then chage the oil all the debris also comes out. when you change the oil in cold condition the debris may stay inside

 

As the others have said, get all the "trash" suspended in the oil by driving the car, and then drain the oil before the "trash" settles back into the bottom of the oil pan.