Car Issues and Fixes

Blue Smoke from the Exhaust – Symptoms and Causes

Avatar Adie Tinkle -

Normal smoke has a light grey, translucent color that is hardly noticeable. For the majority of drivers, the color of the exhaust goes unnoticed until it changes to something else. You might notice it when your car starts to emit blue smoke from the exhaust, accompanied by a burning smell.

Blue smoke emitting from a vehicle’s tailpipe shows that the engine is burning oil. There can be several causes, including worn or damaged piston rings, malfunctioning PCV valves, and defective valve seals. 

To understand the source of blue smoke from the exhaust, we will go through all the potential causes. 

What Makes Exhaust Smoke Blue?

Blue smoke from the exhaust signals that oil is seeping into the combustion chamber, which is burnt along with fuel and air. This occurs mostly because of a faulty engine component that has started to leak. In other vehicles, leaks are caused by natural deterioration of parts. However, in new cars, a defective component is mostly the culprit. 

Causes Behind Blue Exhaust Smoke 

Here is a detailed review of why your exhaust smoke might be blue. 

Blown Head Gasket 

Failure of the head gasket causes oil leakage, which makes its way into the exhaust system and other areas where it shouldn’t be, and there it makes contact with hot surfaces and produces blue smoke. 

Symptoms of Head Gasket Failure 

  • Overheating engine 
  • Power loss 
  • The sweet smell from the exhaust 
  • White or milky discoloration of the engine oil 
  • Loss of coolant without any leaks from the cooling system 

If your head gasket blows, stop driving immediately, as you can cause more damage to the engine. 

Bad Valve Seals 

A properly working valve seal accurately controls the amount of oil entering the cylinders while maintaining the necessary engine compression level by allowing air and fuel to enter. 

Worn-out valve seals allow the oil to enter the combustion chamber unregulated, along with air and fuel. The oil, when burned, creates blue smoke that leaves through the car’s exhaust pipe. 

Symptoms of Bad Valve Seals 

  • Blue smoke 
  • Increasingly poor acceleration 
  • Low power in the engine 
  • Excess smoke when the engine is cold 
  • Ticking sound when accelerating 

If you suspect a bad valve seal is the culprit behind blue smoke from your car’s exhaust, a cold engine test can help you confirm the diagnosis. 

You can also observe blue smoke in the exhaust in the turbocharged system of the car because of a fault. It is mainly related to the cracked turbo that can cause a broken seal in the turbocharger. The turbocharger also forces a high volume of air into the engine, generating an increase in the volume of fuel injected. It leads to more vigorous internal combustion, which leads to more power. 

Worn-Out Engine Oil Seals 

The engine oil needs to reach the engine and lubricate the right components without entering into places such as the combustion chamber. A seal keeps oil out of these places. However, it can wear over time, allowing the oil to leak through them. 

It is crucial to replace malfunctioned seals immediately. Locating them is not an easy job, so it is preferable to take assistance from a professional. 

A special bearing system is present in new turbochargers that help regulate main shaft movement. These bearings depend upon lubrication from a high-pressure film of motor oil. 

Damage to the turbo casing or oil seal in the turbocharge can cause oil to infiltrate rapid air injection to reach the engine’s combustion chamber, where it burns. 

The oil burns with fuel that can cause blue smoke to emit from the tailpipe. Along with blue smoke, other common signs of faulty turbochargers are increased oil consumption, whining noise, or reduced engine power.  

Signs to Diagnose Problems with the Turbo 

Some of the prime symptoms related to damaged oil seal on the turbocharger include 

  • Engine misfires 
  • Turned on engine light 
  • Rough idle 
  • Reduced power when accelerating 
  • Increase blue smoke when accelerating 

Worn Out Rings 

Worn-out piston rings are among the most common causes of blue smoke from your car’s exhaust. They can go faulty along with the valve seals, making the need to be fixed right away. 

Piston rings serve an important function in pulling heat away from the hot piston and onto the chilled cylinder walls that make up the engine block, transferring heat energy into the engine coolant.

When piston rings wear out, it allows combustion gases to enter the crankcase. At that time, fuel and combustion by-products are in the oil, resulting in blue smoke. 

Signs of Bad Piston Rings 

  • Poor Acceleration 
  • Check engine light 
  • Ticking sound when accelerating 
  • The engine feels down on power 
  • Blue smoke coming out of the exhaust 

A simple compression test can help you troubleshoot if blue smoke is coming out of your exhaust as a result of a bad piston. It involves removing one of the spark plugs to accommodate a compression tester. 

Loss of Transmission Fluid 

Low transmission fluid levels can cause smoke from the exhaust. It can be commonly observed in older cars with a vacuum-controlled automatic transmission where a special modulator helps shift gears. In case of a failed diaphragm, the engine can draw more transmission fluid, which burns and appears as blue smoke in the exhaust. 

Signs to Diagnose Transmission Fluid Causing Blue Smoke

If burning transmission fluid is causing smoke from your car’s exhaust pipe, the transmission fluid will be low on the dipstick. It can look discolored and burned, and you might also experience:

  • Poor gear engagement 
  • Burning smells 
  • Transmission leaks under the car
  • Transmission warning light or check engine light 

Low Transmission Fluid

A stuck positive crankcase ventilation (PCV) valve is a potential cause of blue smoke coming from the car’s exhaust because of uncontrolled crankcase pressure. A portion of the engine vacuum is diverted via the PCV valve in order to “Blow by” the combustion gases in the crankcase.

The PCV valve may malfunction, allowing the engine to continuously mix gasoline, air, and oil inside the engine. This can result in blue smoke in the exhaust and other technical issues that might seriously harm the engine.

Signs of Bad PCV Valve 

  • Turned on check engine light 
  • A whistling or hissing sound 
  • Blue smoke coming from the  exhaust 

To diagnose if a bad PCV valve is the cause behind blue smoke coming from the exhaust, you need to start with a visual inspection. Remove the valve and shake it to see if it makes a rattling sound. 

If the valve does not rattle when you shake it, it means it’s likely stuck and needs to be replaced. 

Conclusion

In summary, blue smoke coming from your vehicle’s exhaust should not be taken lightly. It is preferable not to drive your car when you notice blue smoke from the exhaust and take it to a garage as soon as possible. If you keep on driving your vehicle, it can cause significant damage to your vehicle and may even harm the passengers’ life.

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