Why Is My Car Leaking Oil? Common Causes (& How to Fix it)

Oil leakage is bad for the environment and therefore it is important to fix it as soon as possible. Here are the reasons why your car leaks oil

Why Is My Car Leaking Oil

Did you notice oil on your garage floor while the car was parked during the night? Engine oil leaks are pretty common in cars, and some car models leak more than others.

However, engine oil leaks can harm the environment, and it can cause your car to catch fire if the oil is leaking close to a hot exhaust pipe.

In this article, we will go through the most common reasons why your car is leaking oil and how to prevent it in the future. Let’s begin with the most common causes.

10 Reasons Why Your Car is Leaking Oil

The most common reason a car is leaking motor oil is due to a leaking oil drain plug or a leaking oil filter. It can also be caused by a bad valve cover gasket, damaged oil pan, or clogged crankcase ventilation.

These are just the most common reasons, and far from all of them. There could be many different causes and locations of the engine oil leak, so it needs to be visually inspected before replacing any parts.

Here is a more detailed list of the most common possible reasons for an oil leak.

1. Damaged or Rusty Oil Filter

Engine Oil Filter

A faulty or damaged oil filter is sometimes the culprit that causes the oil leak. Check the oil filter to see if it is tightened properly and there are no signs of rust on it. If you find rust on it, it is definitely time to replace both your engine oil and the filter.

The leak can often also come from the O-ring sealing. However, these can be difficult to replace separately, and you may need to replace the whole oil filter.

Please note that the oil filter should be changed every time the oil is changed.

2. Leaking Oil Drain Plug

Oil Drain Plug

The oil drain plug is located at the bottom of the oil sump and is accessible from the vehicle’s underside. A worn or damaged drain plug can cause the oil to leak.

The oil plug sealing or the whole oil drain plug should be replaced every oil change. However, most people skip this and install the old drain plug again. This can cause the oil plug O-ring to leak.

Check and make sure the oil plug is tightened properly, and if it looks like it is leaking from the plug, you might have to replace the gasket or the whole plug.

3. Bad Valve Cover Gasket

Valve Cover And Gasket

Valve covers are located on the top of the engine cylinder head and serve as a seal to prevent oil leakage. The valve cover gaskets tend to wear out after some time because of the heat and the effect that rubbers are getting hardened over time so that oil may drip from them.

The valve cover gaskets are often visible from the outside of the engine, and it is pretty easy to see if the leak comes from there. However, sometimes it can come from the engine’s backside, and you can use a mirror to try to locate any oil leaks from there.

4. Damaged or Rusty Oil Pan

Car Oil Pan

The oil pan is located at the bottom of the engine. It will be damaged over time as debris hits the bottom of the pan and leaves dents.

If you have an aluminum oil pan, there is a risk that you hit something under the car, which caused cracks in the oil pan where the oil leaks from.

If you have a steel oil pan, it is possible that it started to rust for a long time, and after a while, you got a super small rust hole in the pan, which cause the leak.

The leak can also come from the oil pan gasket or the oil pan sealant.

5. Clogged crankcase ventilation

Crankcase Ventilation

The crankcase ventilation makes sure that the car’s compression will not cause an overpressure inside the crankcase.

The crankcase is often ventilated through a valve and a hose going to the intake again.

If the crankcase ventilation is clogged, it can cause overpressure in the engine, and this can be the main reason for several different oil leaks in your car because the oil is trying to find a way out of the engine.

This can easily be identifiable by loosening the oil cap while the engine is at idle. If everything works fine, it should be a slight underpressure there. However, if there is high overpressure there, it might be caused by clogged crankcase ventilation.

6. Damaged Head Gasket

Head Gasket

If the head gasket is damaged, it can cause oil leaks into the combustion chamber or the coolant system.

However, if there is a leak from the oil pressure channels near the edge of the head gasket, it can also cause external oil leaks on your engine.

This is not very common, but it absolutely happens. If it looks like the oil is coming from between the engine block and the cylinder head, it is definitely time to take a look at the head gasket.

7. Crankshaft or camshaft Seals

Crankshaft Seal

Around the crankshaft and the camshaft, seals hold the engine oil inside the engine. As you can imagine, the crankshaft and camshafts are always spinning, and this can cause the sealings to wear out.

The crankshaft has sealings both on the front of the engine, behind the crankshaft pulley, and against the gearbox. If you can see the oil leaking from the gearbox housing, it is likely coming from the crankshaft seal.

The camshaft does often only have sealings on the front of the engine.

8. Leaking Oil Cooler

Engine Oil Cooler

There are two types of oil coolers. Either you have one that is cooled by air, which is often located in the car’s front. The other one is a coolant-cooled oil cooler, which is often located on the engine block.

Commonly, the oil leak is coming from the coolant-coolant type as they often have sealings against the engine block. They are often made of plastic, which can result in cracks of the plastic, which can result in leaks.

Also, the air-cooled ones in the front can leak, so if you see any oil leaks in front of the engine, it is probably coming from the engine oil cooler.

9. Leaking Oil pressure sensor

Oil Pressure Sensor

The oil pressure sensor is often located in the cylinder head or at the engine block. This sensor is often made of plastic, which can cause it to crack and leak within time.

It is often pretty easy to replace once you locate it, and it is often very affordable.

10. Cracked Cylinder Head or Engine Block

Engine Block

This is not common, but it could happen, so it should not be forgotten. If the engine cylinder head or the engine block is cracked, oil can leak from the engine and even enter the cooling system.

This can especially happen if you, by some time, didn’t have enough coolant in the cooling system, which caused the coolant to freeze.

If your cylinder head is cracked, you often have to replace the whole head. If there is a cracked engine block or rust wholes, it is possible to weld it in some rare situations, but often you need to replace the whole engine.

RELATED: Oil Leak Repair Cost – Common Causes & How to Repair It

How to Prevent Oil Leakages?

Regular maintenance and routine oil service are sufficient to keep your car’s engine in good condition and prevent any oil leakage.

It is vital to clean the crankcase ventilation hoses and the control valves sometimes to keep a slight underpressure in your car’s engine. Overpressure will tear on the sealings and create oil leaks.

You can also use special additives that are effective and help to prevent oil leaks. If you want to look at one of these additives, you can find it here at Amazon.

If you notice other symptoms and the problem does not occur in the above-mentioned areas, we advise you to take the car to an authorized dealer for inspection.

Magnus Sellén
Written by:

Magnus is the owner and main author of Mechanicbase. He has been working as a car mechanic for over 10 years, and the majority of them specialized in advanced car diagnostics and troubleshooting. Certified Automotive Diagnostic Technician.

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