Introduction:
In a hydrodynamic journal bearing, the stability of the operating condition is crucial to ensure smooth and reliable operation. When the bearing encounters higher magnitude loads, it can lead to instabilities such as oil whirl and oil whip, which can cause excessive vibration, wear, and potential failure of the bearing. To restore stable operating conditions, adjustments need to be made to the oil viscosity.

Explanation:
The correct answer is option 'B' - oil viscosity is to be increased. This is because increasing the oil viscosity helps to enhance the hydrodynamic film thickness, which is the oil wedge between the journal and the bearing. This film thickness is responsible for supporting the load and preventing direct contact between the journal and the bearing surfaces.

Effects of Increased Oil Viscosity:
Increasing the oil viscosity has the following effects on the hydrodynamic journal bearing:

1. Increased Load Carrying Capacity: When the oil viscosity is increased, the hydrodynamic film thickness increases, resulting in a larger load-carrying capacity. This helps to distribute the load more evenly across the bearing surface and reduce the risk of metal-to-metal contact.

2. Enhanced Damping: Higher oil viscosity leads to increased damping in the bearing system. Damping helps to dissipate the energy generated by vibrations and reduce the amplitude of vibrations, thus minimizing the risk of instability.

3. Improved Lubrication: Higher viscosity oil provides better lubrication between the journal and bearing surfaces. This helps to reduce friction and wear, ensuring smooth operation and extended bearing life.

4. Increased Stability Margin: Increasing the oil viscosity improves the stability margin of the bearing system. The stability margin is a measure of how far the operating conditions are from the onset of instability. By increasing the oil viscosity, the stability margin is increased, reducing the likelihood of instabilities such as oil whirl and oil whip.

5. Reduced Operating Temperature: Higher viscosity oil can help to reduce operating temperatures by improving the heat dissipation capabilities of the bearing. This prevents excessive heat buildup, which can degrade the oil and reduce its lubricating properties.

Conclusion:
To restore stable operating conditions in a hydrodynamic journal bearing when encountering higher magnitude loads, the oil viscosity should be increased. This adjustment leads to an increase in load-carrying capacity, improved damping, enhanced lubrication, increased stability margin, and reduced operating temperatures. These factors collectively contribute to the smooth and reliable operation of the bearing, minimizing the risk of failure and ensuring its longevity.