Dealing with Blue Smoke from the Exhaust: Tips and Techniques

Understanding Blue Smoke from the Exhaust: Causes and Solutions

Seeing blue smoke emanating from your vehicle’s exhaust can be an alarming sight. While it might not be as common as other types of exhaust smoke, blue smoke is often an indicator of a serious underlying issue. In this article, we’ll explore the primary causes of blue smoke from the exhaust, why it occurs, and what you should do if you notice this in your vehicle.

Understanding Exhaust Smoke Colors

Before diving into the specifics of blue smoke, it’s important to understand the significance of different exhaust smoke colors:

White Smoke: Usually indicates the presence of coolant or water in the combustion chamber, often due to a blown head gasket, cracked engine block, or a damaged cylinder head.
Black Smoke: Suggests that the engine is burning too much fuel, which can be caused by a clogged air filter, faulty injectors, or a malfunctioning fuel pressure regulator.
Blue Smoke: The focus of this article, blue smoke is a clear sign that the engine is burning oil. This can result from several issues, each with its own implications for engine health and longevity.

In older vehicle (pre-catalytic converter days), you could see blue smoke from the exhaust the entire time the engine was running. However, if the vehicle is equipped with a catalytic converter, you may only see blue smoke at startup. Once the catalytic converter warms up to operating temperature, it acts like an incinerator to burn off and clean up the exhaust. So you often don’t see the blue smoke after heat up.

Primary Causes of Blue Smoke from the Exhaust

Worn Valve Guides, Worn Valve Stem Seals— When you have worn valve guides or seal, oil can leak down into the cylinder and burn with the air and fuel. The most common symptom of worn valve guides and seals is blue smoke on start-up in the morning, that’s due to oil in the cylinder head leaking down into the cylinder. You see it first thing in the morning because the catalytic converter isn’t yet up to full operating temperature to burn off the excess oil smoke.

Worn Piston Rings — One of the most common causes of blue smoke from the exhaust is worn piston rings. The piston rings are designed to form a tight seal between the piston and the cylinder wall, preventing oil from entering the combustion chamber. Over time, these rings can wear out or become damaged, allowing engine oil to seep into the combustion chamber. When the oil burns along with the fuel, it produces blue smoke.

Signs of Worn Piston Rings

• Blue smoke that intensifies when accelerating.
• Reduced engine performance.
• Excessive oil consumption.

Valve Guide and Seal Wear— Valve seals are responsible for keeping oil out of the engine’s cylinders. They sit on top of the valve guides and prevent oil from dripping down into the combustion chamber. If the valve seals become worn or brittle, oil can seep into the chamber and burn along with the air-fuel mixture, resulting in blue smoke.

Signs of Worn Valve Seals:
• Blue smoke during engine startup, especially after the vehicle has been sitting for a while.
• A noticeable burning oil smell.
• Increased oil consumption.

Blown Head Gasket— Although a blown head gasket often leads to white smoke due to coolant leakage, in some cases, it can also cause blue smoke if the gasket failure allows oil to enter the combustion chamber. A blown head gasket is a serious issue that requires immediate attention to prevent further engine damage.

Signs of a Blown Head Gasket:
• Blue or white smoke from the exhaust.
• Overheating engine.
• Loss of engine power.

Turbocharger Issues— In vehicles equipped with a turbocharger, blue smoke can be an indicator of a turbo failure. The turbocharger operates at extremely high speeds and temperatures, and if its oil seals or bearings wear out, oil can leak into the exhaust system. When this oil burns, it produces blue smoke.

Signs of Turbocharger Issues:
• Blue smoke that appears after accelerating or under load.
• Whistling or whining noises from the turbocharger.
• Loss of engine power or boost pressure.
• Oil leaks around the turbocharger.

Overfilled Engine Oil— While less common, overfilling the engine with oil can also cause blue smoke. If there is too much oil in the engine, it can lead to increased pressure in the crankcase, forcing oil past the piston rings or valve seals and into the combustion chamber.

Signs of Overfilled Engine Oil:
• Blue smoke from the exhaust shortly after an oil change.
• Oil leaking from various engine seals.
• Erratic oil pressure readings.

Worn Cylinder Walls— Similar to worn piston rings, worn cylinder walls can also allow oil to enter the combustion chamber. This is more common in high-mileage engines or those that have not been properly maintained. When the cylinder walls wear down, the seal between the piston and the wall becomes less effective, leading to oil burning and blue smoke.

Signs of Worn Cylinder Walls:
• Persistent blue smoke.
• Loss of engine compression.
• Decreased engine performance.
• Excessive oil consumption.

How to diagnose whether the problem is rings, valve guides or valve stem seals

• A wet/dry compression test determines whether the oil burning problem is ring or valve related— Conduct a dry compression test on all the cylinder and note the readings. Using a pump style oil can, inject about 3 pumps of motor oil into a cylinder and perform another compression test. Repeat the oil injection/compression test individually on the remaining cylinders.

If the compression increases with oil, the problem is worn piston rings. If the compression doesn’t rise, the problem is with the valve guides or valve stem seals.

• A leakdown test determines which cylinder(s) have the bad valves or valve guides. Install a leakdown tester in one cylinder and connect to a compressed air source.

Fit a nitrile or latex glove over the exhaust pipe. If the exhaust valve is leaking the compressed air will fill the exhaust system and inflate the glove. If the intake valve is leaking, you’ll hear the sound of compressed air leaking into the intake manifold.

• Test for valve stem seal leakage. Even a good valve stem seal can leak if the valve guide is worn. But valve stem leaks are most prevalent on older vehicles due to hardening and cracking.

You’ll need a helper in a follower car to conduct this test. A worn valve stem seal will usually produce blue smoke from the exhaust when started first thing in the morning. That’s because the worn seal allows oil to drip past the seal and down the valve guide until the oil pools on the top of the piston. That’s why there’s a cloud of blue smoke on startup.

However, you can confirm even more with this test. Taking advantage of the fact that an engine produces more vacuum when you take your foot off the gas pedal, use this test method. Start the vehicle first thing in the morning. Do not let it warm up.

Take the vehicle for a drive and have your helper follow behind you. Accelerate and then take your foot off the gas. Repeat multiple times. Each time you take your foot off the gas, your helper should notice a puff of blue smoke from the exhaust. This confirms that the valve stem seal has failed. You can try installing new valve stem seals, but if the valve guides are also worn, the new seals will fail and you’ll have blue smoke again.

Fix for oil burning due to worn piston rings

• New or used engine
• Rebuild current engine
• Heavier weight oil will not reduce oil burning due to worn piston rings and can actually accelerate engine wear

Fix for oil burning due to worn valve guides

• Remove cylinder head and have machine shop install new guides or knurl current guides. Install new valve stem seals
• Using a heavier weight oil might slow down oil burning, but also causes additional engine wear

Fix for oil burning due to worn valve stem seals

• Replace valve stem seals.

WARNING: Continuing to drive with blue smoke from the exhaust will result in early catalytic converter failure; an expensive component to replace.

©. 2022 Rick Muscoplat