Solvents vaporize with lower pressure leaving any solids behind. Paint is a good example of a product where the solvent will vaporize at or below atmospheric pressure. In most cases you can reference a vapor pressure chart to learn when the solvent or carrier will vaporize in your application. Viscous Products - Their viscosity usually decreases with an increase in temperature and increases with a decrease in temperature. Oil is a good example of this type of fluid.
High viscosity can interfere with free seal movement and cause seal face contact problems.
Lowering the viscosity can often increase the seal face wear as there is not enough film thickness to keep the surfaces separated. You need a film thickness of at least one micron to keep the lapped seal faces separated. Film building liquids - Petroleum products will form a varnish when first heated and then gradually form a layer of coke as the temperature is elevated. Hard water is another example of a film building fluid. It is black or reddish in color and will be attracted by a magnet.