What causes oil leak under your car? here's what's causing it?

Valve cover gasket; Oil pan gasket or drain plug; Rear main seal; Front crankshaft (timing cover) seal; Oil filter or filter housing; Oil pressure sensor/sender.

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Oil Leak Under Your Car? Here's What's Causing It

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A dark amber-to-black, slick puddle near the center or front of your engine bay almost always means engine oil is escaping a gasket or seal. Most oil leaks start small and get worse over time, so a few spots on the driveway today can become a real problem later. The good news: the fix is usually a gasket or seal rather than major engine work, and you can often narrow down the source by where the drip lands.

Trouble codes you may see

If you scan the car, these are the OBD-II codes most often behind this symptom:

P0520 P0521 P0522P0523P0524

Common causes

1
Valve cover gasket
The most common engine oil leak. Located at the top of the engine, the gasket hardens and cracks with age and heat, letting oil seep down the sides of the engine and onto the exhaust, which causes a burning-oil smell.
2
Oil pan gasket or drain plug
The pan bolts to the bottom of the engine and holds the oil. A worn pan gasket, an over- or under-tightened drain plug, or a missing crush washer drips oil from the lowest point of the engine.
3
Rear main seal
Seals the crankshaft where it exits the back of the engine. Wear, age, or running the engine low on oil can cause it to leak, dripping between the engine and transmission. It's a labor-intensive repair.
4
Front crankshaft (timing cover) seal
Located at the front of the engine behind the harmonic balancer; a hardened seal lets oil leak near the timing cover and accessory belt.
5
Oil filter or filter housing
A loose filter, a missing or doubled-up gasket after an oil change, or a cracked filter housing/adapter (common on some engines) leaks oil at the filter location.
6
Oil pressure sensor/sender
These threaded sensors have a seal that can fail and weep oil; a failing sensor can also set a P0520-series code and give a false oil-pressure warning.

What to do

An oil leak is rarely an emergency, but it's not safe to ignore: oil dripping onto a hot exhaust can smoke or, rarely, catch fire, and a bad leak can run the engine dangerously low on oil. Check your dipstick and keep the level topped up, and slide clean cardboard under the car overnight to pinpoint where the drip lands. If oil is dripping fast, the level keeps dropping, or you see smoke from the engine bay, get it to a shop promptly rather than driving on it.

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Common causes

Valve cover gasket

The most common engine oil leak. Located at the top of the engine, the gasket hardens and cracks with age and heat, letting oil seep down the sides of the engine and onto the exhaust, which causes a burning-oil smell.

Oil pan gasket or drain plug

The pan bolts to the bottom of the engine and holds the oil. A worn pan gasket, an over- or under-tightened drain plug, or a missing crush washer drips oil from the lowest point of the engine.

Rear main seal

Seals the crankshaft where it exits the back of the engine. Wear, age, or running the engine low on oil can cause it to leak, dripping between the engine and transmission. It's a labor-intensive repair.

Front crankshaft (timing cover) seal

Located at the front of the engine behind the harmonic balancer; a hardened seal lets oil leak near the timing cover and accessory belt.

Oil filter or filter housing

A loose filter, a missing or doubled-up gasket after an oil change, or a cracked filter housing/adapter (common on some engines) leaks oil at the filter location.

Oil pressure sensor/sender

These threaded sensors have a seal that can fail and weep oil; a failing sensor can also set a P0520-series code and give a false oil-pressure warning.

What to do