Vehicle coolant is one of the most important operating fluids. Along with changes in the design of engines, the composition of the coolant has also changed. The main function of the coolant is heat transfer (HT). It absorbs up to one-third of the heat energy generated by the engine. The coolant is also responsible for protecting the cooling system from damage caused by corrosion, scaling and deposits. The unfavorable working environment of the engine is also affected by smaller capacities of the cooling systems (CSs) of the drive units, extreme temperatures and increased pressure in the CS, enhancing the importance of the fluid composition. The coolant must be replaced every three years or 100,000 kilometers or every five years or 250,000 kilometers with the Organic Acid Technology (OAT). It is worth remembering that coolant of unknown composition or low quality used for a long time can expose the system to engine overheating, corrosion, deposits and restriction of liquid flow. This can lead to engine failure, in extreme cases even engine seizure. Currently, there are many types of fluids, including nanocoolants with different compositions, that are available on the cooling market. The article presents these fluids, describe the most common failures of CSs, present the currently used methods of fluid replacement in the engine and proposes an innovative method based on the pressure method, which allows both replacing the fluid in the entire system and cleaning it.

This publication presents the results of research aimed at analyzing the dynamic stretching process of multifilament polyester and polyamide threads with medium linear densities. Building virtual design tools for the mechanical properties of textiles under dynamic impact conditions on their structures is a fundamental challenge for identifying textile technological processes and their behavior in real operating conditions. In the Autodesk^® Inventor^® software environment, a virtual analogue model was built based on appropriately connected modules of the Kelvin–Voigt rheological models, for which the input parameters of the selected rheological models were defined. The nonlinear static and dynamic elasticity coefficients were determined based on the obtained results of experimental tests carried out in static conditions on a testing machine at a speed of 33 × 10⁻⁶ m/s and in dynamic conditions on a constructed measuring device. The nonlinear viscosity coefficient was calculated based on data read from the force-time characteristics obtained by measuring forces during stress relaxation in the threads. To conduct this research, an original research stand was designed and built. A series of simulation calculations of the dynamic stretching process were performed for different values of linear densities, lengths of stretched thread sections, and stretching speeds. A comparative analysis of the characteristics obtained from experimental and modeling studies was performed. A very good agreement between the experimental and numerical simulation curves was obtained, which leads to the conclusion about the usefulness of the tools used in the work for the physical description of the thread stretching process.