Oil pans are detachable mechanisms made out of thin steel and bolted to the bottom of the crankcase. To maximize its function, it is molded into a deeper section and mounted at the bottom of the crankcase to serve as an oil reservoir. The oil pan also hosts the oil pump and on the bottom of which is the oil drain plug. When an engine is at rest, the oil pan gathers the oil as it flows down from the sides of the crankcase.

The oil drain plug can be also removed to allow old oil to seep out of the car during an oil exchange. The plug is then screwed back into the drain hole after the used oil is drained out. Drain plugs are usually constructed with a magnet in it, which in turn collects metal fragments from the oil. Other varieties contain a replaceable washer to prevent leakage caused by corrosion or worn threads in the drain hole.

Compared to other automotive parts, an engine oil pan is far more likely to leak. This is because it holds oil being thrown around which eventually finds a leak if there is one. Thus, extra care should be applied when installing an automotive oil pan. Most of the times, the metal at the bolt holes in the oil pan and front cover will be pushed inward around the bolt holes. This is caused by the gasket getting smashed due to their excessive tightening. As the oil pan attempts to stop oil leaks, the gaskets are rendered useless and the oil leak will just get worse. Careful attention must also be placed on the gasket when tightening the bolts and make sure that the gaskets are not being squeezed out from under the oil pan to prevent future oil leaks.