What Causes Oil To Leak From Your Exhaust? (With Symptoms And Fixes)

If there is oil coming out of the exhaust of your car, it can be a sign of serious engine trouble, or it may be a relatively minor issue that can be easily fixed. Either way, oil should not be making its way into the exhaust as it can cause damage to the catalytic converter and oxygen sensors.

Some of the causes of oil coming out of the exhaust of your car include worn valve stem seals, worn piston rings, a clogged PCV valve, a blown head gasket or a too much oil in the engine.

One of the most common causes is a worn valve seal that is allowing oil to leak past it and into the engine cylinder. This will usually result in blue smoke from the exhaust and engine performance issues.

In this article we’ll take a look at the causes of oil coming from the exhaust in more detail and what you can do to diagnose and fix the problem.

What Causes Oil To Come Out Of The Exhaust?

Oil coming from the exhaust of a car can be caused by a number of issues, including worn piston rings or valve stem seals, a clogged PCV valve, engine overfill, or a blown head gasket.

It usually ends up in the exhaust due to being burnt within the engine or if it is forced out due to high pressure.

Burning can occur if the piston rings or valve stem seals are worn or damaged, oil can leak into the combustion chamber when the engine is off or idling. It is then burned along with the fuel, causing blue smoke to come out of the exhaust.

A build up of higher than normal oil pressure can cause excessive pressure to build up in the engine and this can force oil out of the exhaust. Likewise, overfilling the engine with oil or a drop in oil pressure caused by a blown head gasket can also cause oil to be burned in the combustion chamber and come out of the exhaust as blue smoke.

Here are some of the most common reasons why it happens in more detail:

1. Worn Piston Rings

A common cause of oil on in the exhaust is bad piston rings. Piston rings are there to seal the gap between the piston and cylinder wall, preventing oil from entering the engine cylinder.

Worn piston rings can cause oil to leak into the combustion chamber and out of the exhaust. When piston rings wear or become damaged, oil can mix with the fuel mixture and burn up creating blue or grey smoke from the exhaust.

This can also lead to a loss of engine power and an inevitable increase in oil consumption.

2. Damage Valve Seals

Another common cause of oil loss into the exhaust are damaged valve seals. As such, damaged valve seals can also lead to increased oil consumption and decreased engine performance.

Valve seals are responsible for preventing oil from entering the combustion chamber through the intake and exhaust valves.

When valve seals are damaged or worn out, they can allow oil to seep past them and into the engine cylinder. This can cause oil to burn with the fuel and create blue smoke out of the exhaust.

3. Clogged PCV Valve

A blocked PCV valve can also be responsible for oil in the exhaust.

The engine PCV (positive crankcase ventilation) valve is a small, one-way valve that helps regulate the flow of gases in the engine’s crankcase. The PCV valve is typically located on the valve cover or the intake manifold and is connected to the engine’s air intake system. Its primary function is to remove the gases that build up in the engine’s crankcase due to the combustion process.

The PCV valve works by drawing the gases from the crankcase into the intake manifold where they can be burned along with the fuel and air mixture. This helps reduce emissions, prevent oil contamination, and improve fuel efficiency.

The PCV valve also helps regulate the pressure inside the engine, preventing the buildup of harmful gases and reducing the risk of engine damage.

If the PCV valve becomes clogged, it can cause excess pressure to build up in the crankcase, which can force oil out of the engine and into the exhaust system. This will then cause blue smoke from the exhaust and lead to increased oil consumption.

4. Overfilled Oil Level

If the oil level in the engine is too high, it can cause excess pressure to build up in the crankcase, which can force oil out of the engine and into the exhaust system.

It can also cause the oil to be forced past the piston rings and into the combustion chamber. This can cause the oil to be burned along with the fuel, leading to blue smoke coming from the exhaust.

In addition to blue smoke, too much engine oil can also cause other engine problems, such as reduced engine performance and increased engine wear. This is because the excess oil can cause foaming, which can reduce the oil’s ability to lubricate engine components.

5. Incorrect Oil Viscosity

The viscosity of the oil used in the engine can also cause oil to come out of the exhaust. If the oil is too thin, it can leak past the piston rings and valve seals and enter the combustion chamber.

If the oil is too thick, it can cause excess pressure to build up in the crankcase and force oil out of the engine and into the exhaust system.

When the wrong oil viscosity is used, it can also cause increased engine wear, leading to oil leaks and increased oil consumption. This can cause oil to be burned along with the fuel, leading to blue smoke coming from the exhaust.

What Are The Symptoms When There Is Oil Coming From The Exhaust?

When oil starts coming out of the exhaust, it’s a clear indication that something is not right with your engine. Here are some common symptoms that you may experience:

Symptom 1. Blue Smoke from Exhaust

If you see blue smoke coming out of your exhaust, it’s a sign that oil is being burned along with the fuel in the engine. This can be caused by worn piston rings, which allow oil to leak into the combustion chamber.

The oil is then burned along with the fuel, producing blue smoke. Blue smoke can also be caused by a damaged valve seal, which can allow oil to leak into the engine cylinder when the engine is not running.

Symptom 2. Burning Smell from Engine

If you notice a burning smell coming from your engine, it may be a sign that oil is leaking onto hot engine components. This can be caused by a leaky valve cover gasket, which can allow oil to escape from the engine and onto the exhaust manifold.

Symptom 3. Loss of Engine Power

If your engine is lacking performance power, it may be a sign that oil is leaking into the combustion chamber and affecting the engine’s performance.

As outlined above, this can be caused by worn piston rings, which allow oil to leak into the sealed engine cylinder and this reduces the engine’s compression causing a loss or power.

Symptom 4. Decreased Fuel Efficiency

A drop in fuel efficiency is also a sign that oil is leaking into the combustion chamber and affecting the engine’s performance.

This can cause the engine to work harder and use more fuel to produce the same amount of power.

What Next – How To Diagnose And Fix Oil From The Exhaust

Visual Inspection

The first step in diagnosing oil coming out of the exhaust is to perform a visual inspection. Look for any signs of oil leaks around the engine and exhaust system. Check the color and consistency of the oil. If the oil is thick and black, it may indicate a problem with the engine. If the oil is thin and watery, it may indicate a problem with the cooling system.

Inspect the exhaust system for any signs of damage or corrosion. Check the exhaust pipe for any oil buildup or discoloration. If you notice any oil or coolant leaks, it may indicate a problem with the head gasket or other engine components. If you are unable to identify the problem, it may be necessary to take your vehicle to a mechanic for a more detailed inspection.

Compression Test

A compression test can help diagnose problems with the engine that may be causing oil to come out of the exhaust. A compression test measures the amount of pressure in each cylinder of the engine. If the pressure is low in one or more cylinders, it may indicate a problem with the piston rings, valves, or cylinder head gasket.

During a compression test, the spark plugs are removed and a pressure gauge is inserted into each cylinder. The engine is then cranked over to measure the pressure. If the pressure is low in one or more cylinders, it may indicate a problem with the engine. A compression test should be performed by a qualified mechanic.

Leak Down Test

A leak down test is another diagnostic tool that can help identify problems with the engine that may be causing oil to come out of the exhaust. A leak down test measures the amount of air leaking out of the engine through the piston rings, valves, or cylinder head gasket.

During a leak down test, the engine is pressurized with air and the amount of air leaking out of the engine is measured. If the amount of air leaking out of the engine is high, it may indicate a problem with the engine. A leak down test should be performed by a qualified mechanic.

Oil Analysis

An oil analysis can help identify problems with the engine that may be causing oil to come out of the exhaust. An oil analysis measures the amount of contaminants in the engine oil, such as metal particles, dirt, or water.

An oil analysis can help identify problems with the engine, such as worn bearings or piston rings, that may be causing oil to come out of the exhaust. If the oil analysis indicates a problem with the engine, it may be necessary to have the engine rebuilt or replaced. An oil analysis should be performed by a qualified mechanic.

Repair

If you notice oil coming out of your exhaust, there are several repair options available to you. In this section, we will discuss the most common solutions to this problem, including replacing piston rings, replacing valve seals, cleaning or replacing the PCV valve, draining excess oil, and changing oil viscosity.

Replacing Piston Rings

If your engine’s piston rings are worn or damaged, they may allow oil to seep into the combustion chamber and out of the exhaust. To fix this problem, you will need to replace the piston rings. This is a complex repair that should only be performed by a qualified mechanic. The cost of this repair can vary depending on the make and model of your vehicle, but it typically ranges from $500 to $1500.

Replacing Valve Seals

If the valve seals in your engine are worn or damaged, they may allow oil to leak into the combustion chamber and out of the exhaust. To fix this problem, you will need to replace the valve seals. This is a relatively simple repair that can be performed by a competent DIY mechanic. The cost of this repair can vary depending on the make and model of your vehicle, but it typically ranges from $100 to $500.

Cleaning or Replacing PCV Valve

If the PCV valve in your engine is clogged or dirty, it can cause oil to leak into the combustion chamber and out of the exhaust. To fix this problem, you will need to clean or replace the PCV valve. This is a relatively simple repair that can be performed by a competent DIY mechanic. The cost of this repair can vary depending on the make and model of your vehicle, but it typically ranges from $50 to $200.

Draining Excess Oil

If your engine has too much oil, it can cause oil to leak out of the exhaust. To fix this problem, you will need to drain the excess oil from your engine. This is a simple repair that can be performed by a competent DIY mechanic. The cost of this repair is minimal and typically involves only the cost of new oil and an oil filter.

Changing Oil Viscosity

If your engine’s oil viscosity is too high, it can cause oil to leak out of the exhaust. To fix this problem, you will need to change the oil viscosity to a lower grade. This is a simple repair that can be performed by a competent DIY mechanic. The cost of this repair is minimal and typically involves only the cost of new oil and an oil filter.

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