Validation of a Low-Cost Parallel Plate Rotational Viscometer: Effect of Plate Spacing on Viscosity Measurement of Automotive Oils

Abstract Viscosity is the most relevant property of automotive lubricants, directly influencing friction, wear, and energy efficiency of internal combustion engines. This work presents the design, construction, and validation of a low-cost parallel plate rotational viscometer, with emphasis on the systematic analysis of the effect of plate spacing (h) on the measured viscosity. Two commercial lubricants (SAE 15W40 and SAE 20W50) were evaluated for five plate spacings (1.25 mm to 6.25 mm) at room temperature, yielding viscosities of 0.34 ± 0.02 Pa·s and 0.39 ± 0.01 Pa·s at h = 6.25 mm, respectively. The experimental results were compared with literature data from Anton Paar. It is demonstrated that for h ≥ 5 mm, the viscosity values obtained (0.34 ± 0.02 Pa·s for 15W40) are consistent with the reference, while for h ≤ 3.75 mm significant deviations are observed (up to 0.78 ± 0.03 Pa·s for h = 1.25 mm), associated with the increase in shear rate (from 119 s–1 to 594 s–1) and possible nonparallelism effects. It is concluded that the equipment is validated for h ≥ 5 mm, establishing its reliable operating range.