Which gauge should indicate oil pressure shortly after starting the engine?

The oil pressure gauge is the correct choice because it is designed to monitor the pressure of the engine oil in the system, which is critical for the lubrication of engine components. Shortly after starting the engine, the oil pump pressurizes the oil, and the gauge should reflect this pressure almost immediately.

Monitoring oil pressure is essential as it indicates whether the oil is circulating properly and at an appropriate pressure level; inadequate oil pressure can lead to serious engine damage.

In contrast, the water temperature gauge will take some time to register changes in engine temperature, as it reflects how well the engine is being cooled and needs the engine to run for a while to provide accurate readings. The voltmeter, which shows the battery voltage, typically doesn't reflect immediate engine conditions in the same way and may not change significantly right after starting. The fuel gauge is primarily concerned with the level of fuel in the tank rather than engine performance and will not display information relevant to oil pressure immediately after engine start.