Which instrument is typically used to indicate engine oil pressure?

• A. Capsule sensor
• B. Diaphragm with bellows
• C. Bourdon tube
• D. Piezoelectric gauge

Answer: (C)

Oil pressure readouts in engines are typically provided by a Bourdon tube gauge. The curved metal tube inside the instrument tends to straighten as internal pressure increases. That mechanical movement is converted through linkages into a pointer on a calibrated scale, giving a continuous, readable pressure value. This type of gauge handles the engine oil system’s pressure range well, remains rugged under vibration, and doesn’t require electrical power to operate, which is ideal for aircraft engines.

Capsule sensors and diaphragms with bellows are more common in other pressure-sensing contexts or require additional mechanisms to drive a readable display, and they’re not as robust or straightforward for the usual oil-pressure ranges. Piezoelectric gauges generate an electrical signal and are geared toward dynamic pressures and electronic displays, not the simple, direct mechanical indication used for engine oil pressure.