Why Does an Engine Develop an Oil Leak?

In this article from our engine knowledge and vehicle maintenance section, we’ll cover the causes of an engine oil leak. If you’re wondering why a car develops an oil leak, take a look at this article. Now let’s get into why cars leak oil.

Why Does an Engine Develop an Oil Leak?

The causes of an engine oil leak can vary. Since there are many parts in your engine that come into contact with oil, the cause of the leak could be related to any one of them.

The Oil Pan Could Be the Cause of an Oil Leak

One of the causes of an engine oil leak can be the oil pan. The drain plug on the oil pan may be loose, or the plug’s gasket may be damaged. The oil pan itself may have a crack or a hole.

Why Does the Oil Pan Gasket Leak?

If the oil pan gasket is leaking, consider the following possibilities.
The bolts may have loosened.
The gasket may have degraded.
The gasket may not be seated properly.
The pan’s flange may be bent.

Besides these, the oil return passage back to the pan may also be clogged.

If the Camshaft Gear Cover Gasket Is Leaking

The bolts are loose.
The gasket has degraded.
The gasket isn’t seated properly.
The cover’s flange is bent.
The part of the engine the cover mounts to is itself leaking.

Possible Causes If the Front Crankshaft Seal Is Leaking

The oil seal has worn out
The seal was installed incorrectly
The crankshaft journal and pulley bearing surfaces have grooved/worn
The pulley or damper has loosened
The seal or cover has become off-center
The oil return passage to the pan is clogged

Possible Causes If the Rear Main Seal Is Leaking

The seal has worn out
The seal used isn’t the correct type for the application
Rear bearing wear has increased
Grooves have formed on the crankshaft journal

Other Possible Causes of an Engine Oil Leak

An engine oil leak can also occur because the plug at the rear of the camshaft isn’t tight enough or wasn’t seated properly, its bore has become damaged, or the camshaft’s end-play has increased.

One of the oil system’s external fittings could be leaking.
The oil filter can also be the cause of an engine oil leak. The oil filter itself may be leaking.
The distributor housing may be leaking oil.

The Valve Cover Can Also Be the Cause of an Oil Leak

A car can leak oil due to loose mounting bolts, a damaged or improperly seated gasket, or bent edges on the cover. (On L-type engines)

An engine can leak oil because the rocker cover’s bolts are loose, the gasket is torn or isn’t seated properly, or the edge of the cover is bent.

On engines with an externally mounted oil pump, the pump’s mounting bolts may be loose or its gasket may have degraded.

A failure in the crankcase ventilation system, or a clogged ventilation hose, causes pressure inside the crankcase to build up, which can also result in an oil leak.

If the oil pressure relief valve is mounted on the outside of the engine, its bolts may be loose, or its gasket may be damaged. This can also cause the car to leak oil.

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