Rheological Characterization of Automotive Hydraulic Fluids and Biodegradable Oil

Automotive fluids are fundamental to the safe and efficient operation of vehicles, as they transmit energy, provide lubrication, protect against corrosion, and ensure the stability of critical systems. Among them, brake fluid plays a vital role by transmitting hydraulic pressure within the braking system, guaranteeing safety and immediate response. Similarly, power steering fluid enhances vehicle maneuverability by reducing friction and wear in pumps and valves. The physicochemical and rheological characterization of these fluids is essential for evaluating their performance and exploring environmentally friendly alternatives. The primary objective of this work is to analyze the physicochemical and rheological behavior of conventional automotive hydraulic fluids and an unmodified canola oil baseline. Rather than proposing an immediate replacement, the study aims to quantify differences in viscoelastic response and thermal sensitivity to identify future modifications. The experimental focus is a detailed rheological comparison of representative commercial products (DOT 3 brake fluid and an STP power‑steering fluid) against the canola sample. To achieve this, the fluids were characterized through FTIR spectroscopy, density measurements, viscosity index determination, and comprehensive rheological testing. The rheological characterization was conducted in a Discovery HR-3 Hybrid Rheometer using three complementary approaches: thermo-rheological evaluation, steady-state flow tests, and oscillatory tests, providing a robust framework for comparing conventional automotive fluids with sustainable alternatives. The results reflect the functional requirements of each system: stability and safety in the brakes; protection against cold and hydraulic performance in the steering. Commercial fluids meet the operational requirements and identify the modifications needed to move toward viable plant-based formulations.