There is no relationship between the viscosity and density of a fluid. While viscosity is the thickness or thinness of a fluid, density refers to the space between its particles. However, both properties are affected by temperature. When a fluid is heated, its particles move far apart, and it also becomes less viscous.
A liquid that is dense does not necessarily have to be viscous, and the opposite is also true. For example, honey is more viscous than saline water, but it is not as dense. Viscosity can be defined as the speed of the flow of a liquid. It is the measurement of the shape of molecules and the intermolecular forces. When a viscous liquid is heated, its speed of flow is increased, but the density still remains largely the same. The relationship between viscosity and temperature is the principle behind the technology of manufacturing vehicle lubrication oils. However, density is the mass per unit volume of a liquid. It is loosely referred to as the weight of a liquid. It is determined from the equation that density equals mass divided by volume. The two properties are very different concepts, but together, they can describe more than half of a fluid’s characteristics. Since there is no relationship between the two, the maxim that heavier fluids are more viscous is misleading.