Oil Pan

The oil pan (also known as the oil sump) is a metal or high-strength plastic pan bolted directly to the bottom of the engine block. It seals the bottom of the engine crankcase and serves as the primary reservoir for engine oil when the engine is not running, and collects the oil as it drains back down from lubricating the cylinder walls, bearings, and valvetrain during operation.

Inside the oil pan, the oil pick-up tube is submerged, allowing the oil pump to draw pressurized oil to distribute throughout the engine. The oil pan also features a threaded drain plug at its lowest point, which is removed during routine oil changes to drain the old engine oil. Many modern oil pans also house the engine oil level sensor or oil temperature sensor.

Because it is located at the absolute bottom of the engine bay, the oil pan is highly vulnerable to damage. Road debris, hitting a curb, or bottoming out can dent or crack a metal pan, or puncture a plastic pan, leading to rapid oil loss. Rust and corrosion can also cause thin spots in steel pans, leading to pinhole leaks. Additionally, the gasket sealing the pan to the engine block can degrade, causing persistent oil leaks.

If an oil pan is cracked or leaking severely, it must be replaced or resealed. Servicing the oil pan requires draining the engine oil, unbolting the pan, cleaning the mating surfaces of the engine block, applying a new gasket or silicone sealant (such as RTV), and torqueing the bolts to specification to prevent leaks.