Measuring the Viscosity of Motor Oil
Laboratory Assignment #1
An experiment was conducted to model the effect of temperature on the viscosity of motor oil and compare the results to commercial values established by the Society of Automotive Engineers (SAE) for SAE 30, SAE 40 and SAE 5W30.
The viscosity of the oil sample at eight temperatures between 20 °C and 55 °C was determined using a rotary Brookfield DV-II+ viscometer. The temperature of the oil sample was controlled by the circulation of water from a Brookfield TC-502 water bath temperature controller through a water jacket assembly around the oil chamber. This type of viscometer measures the torque required to rotate an immersed spindle in a fluid.
Overall, the experiment yielded appropriate results: the viscosity of the oil sample decreased as temperature increased. However, upon research, none of the three SAE motor oil viscosity ratings were within the uncertainty of ±1% of the full-scale viscosity value of the oil sample at the given temperature. The motor oil that did match the tested sample within ±1% was SAE 10W40. The next closest was SAE 30 at ±10%. If the possible motor oils are restricted to SAE 30, 40, and 5W30, it can be concluded that it was likely SAE 30.
Motor oil is crucial for reducing excess heat due to friction in internal combustion engines and ensuring optimal performance and minimal wear. As engine lubrication is a highly important and relevant subject, efforts were made to explore how motor oil viscosity varies with temperature. To this end, a rotary Brookfield DV-II+ viscometer was implemented to measure the dynamic viscosity of a sample of motor oil at eight different temperatures between 20°C and 55°C. The device calculated the viscosity by measuring the torque required to rotate a spindle immersed in the oil at a given RPM, taking into account the geometry of the spindle and the type of container used for the oil. The viscometer was accurate to within ±1% of the full-scale viscosity value for a given spindle geometry and RPM, while the uncertainty for the temperature probe immersed in the oil was ±1°C.
The temperature of the motor oil was regulated by passing temperature-controlled water through a water jacket assembly that encased the oil container. The oil viscosity, the torque and RPM of the rotating spindle, and the full-scale viscosity value were recorded for each of the eight temperatures. A plot of motor oil viscosity versus temperature was then made. Dynamic viscosity values for SAE 30, SAE 40, and SAE 5W30 were tabulated and compared to the data collected during the experiment.
It was predicted that the oil viscosity and the oil temperature would have an inverse relationship. The objective of the experiment was to not only prove that this was the case, but also to examine the specific behavior of the oil under different conditions. The importance of this experiment was the identification and understanding of the relationship between viscosity and temperature and how this can affect systems that use motor oil in real world environments.
Table 1. Commercial Values for Dynamic Viscosity 
| SAE 40
| SAE 5W30
85.9 @ 40°C
| 136.2 @ 40°C
| 61.98 @ 40°C
Table 2. Experimental Values for Temperature, Full Scale Viscosity, and Absolute Viscosity
| Absolute Viscosity (mPa·s)
| Full Scale Viscosity (mPa·s)
Figure 1. Illustration of Inverse Relationship between Temperature and Absolute Viscosity
The effect of temperature on the viscosity of a given oil sample was observed during this experiment and the values compared to various dynamic viscosity values of...
Please join StudyMode to read the full document