Put a few drops of liquid on a horizontal surface and then tilt the surface. The liquid will begin to flow downhill. The more viscous the liquid, the more slowly it will move. Try this experiment with different liquids such as honey, glycerine and oil. Try a single liquid at different temperatures and compare the results.
Most liquids are less viscous at higher temperatures.
This is a problem is some situations. An automobile engine is cool or cold when the car is turned off, but gets very hot inside when it has been running for a while. The oil used to lubricate the engine has to maintain viscosity at high temperature but not get so thick at low temperature that it interferes with the operation of the engine. Multigrade oils include additives that help them retain a relatively uniform viscosity over a range of temperatures. Viscosity and Density Density is mass per unit of volume.