You will recall the packing generates almost six times the heat of a balanced mechanical seal If you are not using a dual seal with a pressurized barrier fluid, then you will get some sort of a pressure drop across the seal face. As the product passes across the faces a cooling occurs, causing the faces to close. When the faces close, the cycle repeats its self and the alternating closing and opening will probably crack the carbon as it bangs against the drive lugs or chip the carbon face on the outside diameter. If the product freezes when it evaporates it could freeze any oil or grease that was put on the seal face, causing damage to the carbon. Cause the liquid to solidify.
Paint is a mixture of a solid and a solvent.
If the solvent evaporates, the paint will solidify between the faces. Some liquids will form a film at the faces if the pressure drops If the temperature or pressure of the pumping fluid never changed we would seldom have any application problems. The cooling jacket must be free from scale and calcium build up. There are many cleaning products on the market you can flush through the jacket to insure that it is clean with out having to disassemble the pump. Check carefully because some of these lines can be hidden by insulation.