Using the oil chart provided in the illustration for guidance, what would be the recommended straight weight petroleum oil to use in a main engine speed control governor on your fishery research vessel, if the governor is to remain in the acceptable operating range and the governor oil operating temperature may drop as low as 40°F? Illustration MO-0161
• Use the oil chart for petroleum oils only, not synthetic or transmission fluids • Focus on the temperature range that includes 40°F and stays inside the hatched “acceptable operating range” band, not just ‘limited’ operation • Notice that straight-weight oils (SAE 10, 20, 30, 40) all have different low‑temperature limits on the chart
• On the petroleum oil section of the chart, which straight‑weight grade is still within the acceptable operating range at 40°F, rather than only in the limited low‑temperature zone? • If your minimum expected temperature is 40°F, what happens to viscosity if you choose an oil whose acceptable operating band starts well above 40°F? • Compare the low‑end limits of SAE 10, 20, 30, and 40: which one keeps the governor oil in the central ‘ideal’ band at 40°F and not close to the pour‑point end?
• Verify the left‑hand (low temperature) boundary of each straight‑weight petroleum oil bar relative to 40°F • Confirm that at 40°F the oil is within the ideal or broad acceptable operating range, not just marginal low‑temperature operation • Double‑check that the chosen grade does not exceed the recommended upper limit for petroleum oil (about 200°F) over the likely operating temperatures
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