Oil pressure relief valve

It lubricates internal components, like the crankshaft, camshaft, piston rings, and valve train, to reduce friction and keep things cool during operation. It also helps keep the engine clean by carrying contaminants to the oil filter and prevents corrosion. When you start your engine, the oil pump draws oil from the sump and pushes it through oil galleries—narrow passages you might envision as the arteries of the engine. As the oil flows through the system and encounters resistance from moving parts, pressure builds. To keep your engine running properly, oil circulation and pressure must be kept in check. This job is performed by a small, crucial device called an oil pressure relief valve.

The relief valve uses a simple spring/plunger mechanism and looks a bit like an oversized chess piece. When oil pressure exceeds a preset limit determined by the engine’s manufacturer, it overcomes the spring tension, opening the valve and allowing excess oil to flow back to the sump. Once the pressure returns to the normal operating range, the valve closes again. Pressure is monitored via a gauge on your instrument panel, and how it’s displayed depends on the type of system installed in your aircraft (i.e., EFIS, analog gauges, or some hybrid setup).

It’s normal for oil pressure to spike on cold start when the oil is still viscous and holds a low temperature or when engine rpm increases and more oil is pushed through the system. But as the engine warms up and the oil thins, pressure should settle into the expected operating range. If you notice fluctuating or rising pressure values that exceed the normal operating range after startup, shut down to prevent engine damage. While the culprit could be a faulty sensor or gauge, the relief valve could be sticking or worn out. Check your oil levels, consult your POH to confirm the numbers you should be seeing, and call your mechanic. You might surprise them with your newly acquired knowledge of this unassuming component, and a simple swap might be all that is needed to get you back in the air.

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