An engine oil leak shows up as amber to black, slick drips under the engine, a burning oil smell, or an oil level that keeps dropping. The most common sources are the valve cover gaskets, the oil pan gasket and drain plug, the oil filter, and the front and rear crankshaft seals. A rear main seal leak drips from where the engine meets the transmission and is the most expensive to fix, because the transmission has to come out to reach it.
Where the oil is coming from
| Source | Where you see it |
|---|---|
| Valve cover gasket | Oil around the top of the engine and down its sides, often with a burning smell from the exhaust |
| Oil pan gasket or drain plug | Wet oil pan and drips directly under the engine |
| Oil filter | Oil around the filter, from a loose filter or a doubled old gasket |
| Front crankshaft seal or timing cover | Oil at the front of the engine behind the balancer pulley |
| Rear main seal | Oil dripping from the bottom of the bellhousing, between engine and transmission |
| Oil cooler lines or pressure sender | Wet lines or fittings |
Valve cover gasket leak
Valve cover gaskets harden and shrink with heat and age. Oil seeps out at the top of the engine and runs down, and if it reaches the exhaust manifold it smokes and smells; see burning smell from car. It is usually one of the easier and less expensive leaks to fix.
Oil pan gasket leak
A leaking pan gasket or a drain plug with a worn or missing washer leaves a wet pan and drips under the engine. On some vehicles the pan is easy to reach; on others the subframe or exhaust has to be moved.
Rear main seal leak
The rear main seal seals the back of the crankshaft where it leaves the engine. A leak shows as oil dripping from the bottom of the bellhousing. Because the transmission, and on manual cars the clutch, must come off to replace it, owners often do it at the same time as a clutch or transmission replacement. Check the fluid color first: red fluid in the same spot is more likely the transmission front pump seal; see transmission fluid leak.
How to find an oil leak
- Clean the engine so fresh oil shows where the leak starts.
- Slide cardboard under the car overnight to see where drips land.
- Add UV dye to the oil and trace it with a UV light after a drive.
- Remember that oil runs down and back with airflow, so the highest wet point is usually the source.
How serious is it?
A slow seep that never lowers the level is a nuisance; a leak that drops the level, drips onto the exhaust or soaks the belts needs prompt repair. Keep the oil topped up, because running low causes low oil pressure and bearing damage. Stop-leak additives are only a temporary measure. If the engine also burns oil or knocks, see how to tell if an engine is blown and our engines.
More guides: synthetic vs conventional oil · valve cover gasket leak · rear main seal leak · oil pan gasket leak.
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