Yes, pumping and mixing polymer-modified bitumen at 120-140 °C can be problematic, and this is a well-known operational issue. At these temperatures, the viscosity of PMB is often still very high and strongly non-Newtonian, especially for SBS systems, which leads to poor pump efficiency, high pressure drop, and risk of cavitation or polymer separation in low-shear zones. Mixing also becomes less effective, so you can get incomplete dispersion and local overheating. That is why most plants handle PMB at 160-180 °C during production and only cool to 120-140 °C for short-term storage or transfer with specially selected pumps.