What condition is likely to cause fluctuations in fuel oil pressure?

• A. High ambient temperature
• B. Cold oil in the suction line
• C. Faulty pressure gauge
• D. Excessive throttling

Answer: (B)

Cold oil in the suction line is likely to cause fluctuations in fuel oil pressure due to the increased viscosity of oil at lower temperatures. When oil is cold, it becomes thicker, which can impede the flow rate and create resistance as it travels through the system. This resistance can lead to variations in pressure readings as the oil struggles to move through the line. As the temperature of the oil increases, its viscosity decreases, allowing for a more stable flow and consistent pressure readings.

In the context of the other conditions: high ambient temperature can lead to a decrease in oil viscosity, potentially stabilizing pressure; a faulty pressure gauge may give inaccurate readings without actually affecting the oil pressure itself; and excessive throttling can impact pressure but is typically more associated with pressure drops rather than fluctuations. Thus, the characteristics of cold oil directly contribute to the instability in fuel oil pressure.