Normal exhaust smoke is a barely visible semi-translucent shade of light gray. For most drivers, the color of their exhaust goes unnoticed right up until something changes.
You’ll certainly take notice when your car’s exhaust start emitting blue smoke accompanied by a burning smell.
Blue smoke emitted from a vehicle’s tailpipe usually means that the engine is burning oil, and can be attributed to a variety of factors such as worn or damaged piston rings, defective valve seals, or a malfunctioning PCV valve.
To troubleshoot why your car has blue smoking coming from the exhaust and how to fix it, we’re going to have to have to pop the hood on all the potential causes.
What Color Should Exhaust Smoke Be?
Normal car exhaust from a gasoline engine is translucent to barely visible to perhaps wisps of light gray. In temperatures that are above freezing, it’s barely visible and can turn opaque as the mercury drops. This is usually due to miniscule amounts of water vapor condensation coming out of the car’s exhaust system.
What Does Blue Smoke Mean?
Blue smoke coming from the exhaust is often a sign that the engine is burning oil or some other contaminant has gotten into the internal combustion chamber and/or the car’s exhaust system. There might also be an issue with the positive crankcase ventilation valve that’s failed to regulate the pressure in the crankcase itself. As the fuel and oil mixture combusts, it produces blue smoke which is expelled through the exhaust pipe.
Though the reason why the car is burning oil is of even more serious concern, some can be major mechanical faults such as a cracked cylinder head’s valve guides or you have bad piston rings.
Top 5 Possible Causes of Blue Smoke from Exhaust
Dialing in on what’s causing blue smoke from the car’s exhaust is essential for knowing just what you need to repair. Even if it’s something you can’t repair on your own, knowing the underlying cause can save you some labor costs in the final mechanic’s bill.
1. Bad Valve Seals
Blue smoke in the exhaust can be caused by bad valve seals allowing too much oil to enter the cylinders during the internal combustion process. Normally functioning valve seals precisely control the amount of oil entering the cylinders while also helping to maintain necessary engine compression levels by allowing air and fuel to enter.
When valve seals fail, oil enters the combustion chamber unregulated, along with air and fuel. It is then burned, which creates blue smoke that exits via the car’s exhaust pipe.
Signs of Bad Valve Seals
Sometimes when a check engine light comes on due to bad oil seals causing blue smoke from the exhaust, the ECU will also throw codes P0075 through P0086. Though these are generic exhaust valve codes.
How to Diagnose Bad Valve Seals with a Cold Engine Test
If you suspect that bad valve seals are the cause of blue smoke from your car’s exhaust, a cold engine test will help confirm the diagnosis.
This starts with letting your car sit overnight. The top of the cylinder head of the valve cover will still have some residual oil remaining from the last time you drove.
Then when you start the engine, this oil is drawn down through the bad valve seal into the combustion chamber. This produces a massive belch of blue smoke from the exhaust before normalizing. You might only notice wisps of blue smoke at that point as the seals attempt to operate normally.
How to Fix Bad Valve Seals
You might be able to pull off some short-term fixes to buy you some time to save up enough money to repair your bad valve seals.
Our Product Choice: BlueDevil 49499 Oil Stop Leak
If you notice signs of blue smoke in your exhaust early, and the valve seals are just starting to go bad, you might be able to remedy the problem in the short term by adding oil-stop-leak to the oil reservoir. This is in addition to changing the oil to high mileage viscosity.
It’s specially formulated to extend the life of a car’s valve seals by causing the rubber to swell. If the problem with your valve seals is minor, this can temporarily reduce the oil leak for a few weeks or even months.
Though if the valve seas are badly worn out, cracked, or badly damaged, adding oil stop-leak will have no appreciable effects.
The Cost to Fix Bad Valve Seals
The cost of the valve seals themselves is relatively low. However, most of the repair cost will be in the mechanic’s labor.
The cost to fix your bad valve seals will run between $900 to $2,000, depending on the make and model of the vehicle.
2. Worn Out Rings
Worn-out piston rings are another common cause of blue smoke coming from the exhaust. Sometimes they will go bad right along with valve seals, and both will need to be fixed at the same time.
Piston rings play an important role in drawing heat away from the hot piston into the cooled cylinder walls that make up the engine’s block as it builds up the heat energy transfers into the engine coolant.
When piston rings wear out, combustion gases enter the crankcase. At the same time, fuel and combustion by-products are in the oil, resulting in blue smoke.
How to Diagnose Bad Piston Rings
A simple compression test will help you troubleshoot if the cause of blue smoke coming out of your exhaust is due to bad piston rings. This involves removing one of your spark plugs to accommodate a compression tester.
Then try to start the engine while someone writes down the results of the compression tester. You can then compare this to the compression stats listed in the car’s owner’s manual or the repair guide.
You can buy an inexpensive compression tester online or at most auto parts stores.
Our Product Choice: BETOOLL HW0130 Petrol Engine Cylinder Compression Tester Kit
Our Product Choice: OTC 5605 Gasoline Engines Compression Tester Kit
How to Fix Bad Piston Rings
The only permanent fix for bad piston rings that are causing blue smoke from the exhaust is replacing them. Replacing new piston rings is rarely the sort of thing that a DIY mechanic can or should do on their own. It requires some special tools and there’s a lot of labor involved. At the same time, worn-out piston rings often cause problems with other engine components that need to be repaired by a professional mechanic.
The cost to have a mechanic replace worn-out piston rings ranges from $1,500 to $2,800.
3. A Problem with the Turbo
A fault can sometimes cause blue smoke in the exhaust in the turbocharging system of a car with a turbo-enhanced engine. This is usually related to a cracked turbo casing or a broken oil seal in the turbocharger.
A turbocharger forces a higher volume of air into the engine, increasing the volume of fuel injected. This makes for more vigorous internal combustion, which in turn produces more power.
A lot of newer turbochargers have a special bearing system that helps regulate main shaft movement. These bearings rely on lubrication from a high-pressure film of motor oil.
If the turbo casing or the oil seal in the turbocharger is damaged, this oil can infiltrate the rapid air injection to reach the engine’s combustion chamber, where it burns. This oil will then burn along with the fuel, causing blue smoke to be emitted from the tailpipe. In addition to blue smoke, other symptoms of a faulty turbocharger can include reduced engine power, a whistling or whining noise, and increased oil consumption.
How to Diagnose a Problem with the Turbo
Diagnosing a problem with the turbo related to a failed oil seal that causes blue smoke starts with recognizing the overt symptoms. This includes:
The check engine light can come on when a turbocharger malfunctions due to insufficient compression. Sometimes this causes the ECU to throw a P2262 code for “Turbo Boost Pressure Not Detected-Mechanical.” While this is a blanket code for a turbocharger problem, it definitely narrows the issue down when you’re trying to find the cause of blue smoke coming from the exhaust.
Sometimes you might also get a P0299 code if the ECU detects an under-boost condition while the turbocharger or supercharger is operating.
How to Fix a Bad Oil Seal on a Turbo
If your turbo is leaking oil causing blue smoke to come from your tailpipe and affecting engine performance, the best fix is usually to replace the turbocharger altogether.
Though what really matters here is that an oil seal failure on a turbo is usually a symptom of another problem. Often there’s something wrong in the oil system, such as a bad oil line or another mechanical failure. So, you shouldn’t be surprised if your mechanic recommends additional repairs.
The cost to have a mechanic replace a turbo can vary wildly from as little as $750 to as much as $2,500. The biggest factor is the amount of labor it might take for the mechanic to access the turbocharger, as well as any other oil system repairs that might also need to be made.
Can I Replace a Turbocharger Myself?
Replacing the actual turbocharger part isn’t all that complicated. The issue is that a lot of modern car manufacturers put turbochargers in places that aren’t easy to access. This might call for a significant amount of other parts needing to be removed to access the turbocharger and the lines properly.
Compound this with the fact that a failing turbocharger usually has other complicated repairs required in order to 100% address the cause of the blue smoke coming from the exhaust. So, it’s usually best to leave a turbocharger replacement to a professional mechanic.
4. A Loss of Transmission Fluid
low transmission fluid levels can also cause blue smoke from the exhaust. This is more common in older cars with a vacuum-controlled automatic transmission where a special modulator is used to help shift gears. If the modulator suffers a failed diaphragm, the engine can draw in transmission fluid, which burns and appears as blue smoke in the exhaust.
How to Diagnose Transmission Fluid Causing Blue Smoke
If your engine is burning transmission fluid, causing smoke from your car’s exhaust pipe, the transmission fluid itself will be low on the dipstick. It might also look burned and/or discolored. You might also experience:
How to Fix Burning Transmission Fluid
If the cause of the blue smoke coming from the exhaust is directly linked to burning transmission fluid, you’ll likely need to have the transmission modulator replaced. Your mechanic will probably also need to change the vacuum line, which is usually compromised or fouled as well.
Replacing the transmission modulator requires opening up the transmission, which automatically means at least $350 to $500 in labor alone.
You can expect the final cost to have the transmission modulator and vacuum line replaced to range between $750 to as much as $1,500.
5. A Stuck or Bad Positive Crankcase Ventilation Valve
A stuck PCV valve is another potential cause of blue smoke coming from the car’s exhaust due to uncontrolled crankcase pressure. The positive crankcase ventilation (PCV) valve diverts some of the engine vacuum to draw or “Blow-By” the combustion gases in the crankcase.
It’s possible for the PCV valve to fail to cause the engine to continually mix oil with air and fuel inside the engine. Not only can this cause blue smoke in the exhaust, but it can lead to a variety of other mechanical problems, which can cause major engine damage.
Signs of a Bad PCV Valve
How to Diagnose a Bad PCV Valve
Diagnosing if a bad PCV valve is causing blue smoke to come from the exhaust starts with a visual inspection. You want to look at the hoses connecting to the crankcase. Remove the valve and shake it to see if it makes a rattling sound.
If the PCV valve doesn’t rattle when you give it a good shake, then it’s likely stuck and will need to be replaced.
Common codes which could also indicate that a bad PCV valve is causing blue smoke to come out of the exhaust include code P053A for a Positive Crankcase Ventilation Heater Control Circuit /Open. You might also get a P0171, meaning the Fuel System is running too lean. Though a P0171 on its own can be a lot of things and doesn’t immediately scream a bad PCV valve.
How to Fix a Stuck PCV Valve
Fixing or replacing a stuck PCV valve is something most DIY mechanics can handle on their own. You’ll need to source the correct replacement valve and then use the following steps.
Frequently Asked Questions
Is Blue Smoke from Exhaust Bad?
Blue smoke coming from your exhaust is usually a sign of a serious problem. Most of them, like a bad PCV valve, piston rings or worn-out valve seals, can cause serious damage.
What Makes Blue Smoke from Exhaust When Starting?
Bad piston rings, worn-out valve seals, or a stuck PCV valve are the most common causes of blue smoke from the exhaust on startup.
What Makes Blue Smoke From Exhaust When Accelerating?
Blue smoke from the exhaust when accelerating is often a sign of worn-out oil seals allowing the engine to burn oil.
Can You Drive with Blue Smoke Coming from the Exhaust?
Most of the things that cause blue smoke to come from the exhaust are serious enough that you probably shouldn’t drive the car until you get it fixed. You might be able to limp home or to the mechanic if the problem is limited to the early stages of bad valve seals, a stuck PCV valve, or a crack in the turbo oil seal. Just be sure to check your oil and transmission fluid. If they’re dangerously low, try to top them at least up while limping to your destination.
If the engine is misfiring, stalling, and running very hard, or you hear the transmission gear grinding, then it’s better to pull over. The cost of a tow truck is inevitably going to be much lower than the severe damage these symptoms can cause.
Conclusion
The most common cause of blue smoke coming from the exhaust is a stuck PCV valve, worn-out valve seals, or bad piston rings, allowing the engine to burn out. Though a cracked oil seal in the turbocharger can also let oil into the combustion chamber, causing blue smoke.
If you have an older vehicle and you notice that the transmission fluid is low or looks dark, you might have a bad modulator. If you’re lucky, and it’s a stuck PCV valve, you might be able to make the fix yourself for less than $100. If the valve seals have just started to wear out, some oil stop leak might buy you a few weeks to save up for a more expensive repair.
Otherwise, you should expect that you’ll need to have the valve seals or the piston rings, or the turbocharger completely replaced at a cost pushing or exceeding $1,000 or more.
Written By
Jason Farrell
Jason Farrell is a certified master technician, the editor of Mechanic’s Diary in Pittsburgh, Pennsylvania. He is ASE (Automotive Service Excellence) certified and earned a Bachelor’s Degree in Automotive Technology from Pittsburg State University. With nearly 18 prior years of experience in the automotive field, he has extensive knowledge about Domestic, European, and other foreign makes and models of cars and light trucks. Jason’s experience working as a technician and service manager at dealerships, gave him the experience and know-how of most aspects of inspection, diagnosis, and repair from engine and drivability to electrical, HVAC, brakes, steering and suspension and everything in between.