FAA Powerplant Written Practice Test

Where is the oil temperature bulb located on a dry sump reciprocating engine?

1. At the main oil filler

2. In the oil outlet line

3. In the oil inlet line

4. At the oil cooler output

The correct answer is: In the oil inlet line

In a dry sump reciprocating engine, the oil temperature bulb is located in the oil inlet line. This placement is important because it allows for accurate measurement of the temperature of the oil returning from the lubrication system to the engine. Monitoring the oil temperature at this point helps in assessing the performance and efficiency of the lubrication system, ensuring that the engine is operating within safe temperature limits. The oil temperature bulb must be positioned in the inlet line to capture readings that reflect the oil’s condition before it circulates back into the engine, thus providing vital feedback on the oil's thermal management. This is crucial for preventing potential overheating, which could lead to engine damage. While other locations such as the main oil filler or oil cooler output may seem viable, they do not accurately reflect the temperature of the oil being fed back into the engine. Similarly, the oil outlet line primarily deals with oil being expelled from the engine rather than what is entering it, making the inlet line the optimal position for temperature measurement in a dry sump system.