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What Are The Causes of Smoke Coming Out of Exhaust?
If you have started to notice that you are having smoke coming out of your exhaust when your vehicle is running there can be many different causes for why that may be happening.
It mainly depends on what color the smoke is that is coming out of your exhaust as to what you first should start looking at. I’ve included the three main smoke colors that you can see when smoke does come out of your exhaust and the most common fixes for each color smoke.
White Smoke Coming Out Of Exhaust
It’s normal to see some white smoke when you first start up your vehicle from a cold start. This is just water vapors that have been sitting in the system while the car was off. Once your car gets up to the normal operating temperature you should no longer see white smoke coming out of your cars exhaust unless it is very cold out.
If you continue to see white smoke coming out of your exhaust you would want to pull over until you can figure out what is going on.
Head Gasket
The main cause for seeing white smoke coming out of your exhaust is going to be that you have a failed head gasket. An engine head gaskets’ main purpose is to seal the upper part of your engine to your engine block so that no coolant or oil is allowed into the cylinder walls.
If your head gasket is failing it can start to allow coolant from your coolant system to flow into the cylinder walls that will eventually be pushed out of the exhaust via the combustion process in the form of white smoke.
If you suspect that your head gasket is going out you would want to get it replaced which is not that easy of a job. The gasket itself is pretty cheap to replace but to remove the top part of your engine to replace the gasket is going to cost a bit of cash. The typical head gasket replacement cost can be anywhere from 1,000 to 2,000 dollars.
Cracked Cylinder Head
Other causes of white smoke coming out of your exhaust can be a cracked cylinder head or a cracked engine block. If your cylinder head is cracked that can also allow coolant to seep into the walls of your cylinder and eventually mixed into the fuel and air mixture. If your cylinder head is needing replacement you can replace your cylinder head of your engine from anywhere from 200 to 300 dollars.
Cracked Engine Block
If you suspect that the engine block of your car is cracked you may want to look at replacing the whole engine at that point. Replacing the block of your engine is going to be one of the most expensive repairs that you can have done to your engine.
This is because an engine cylinder block is basically the whole bottom part of your engine and makes up most of the size of your vehicle’s engine. If you have a cracked engine block you are likely going to be better off in buying a new engine for your car or replacing your current engine with a used engine from a local junk yard or off of ebay.
Replacing your engine block will typically cost around 1,500 dollars which may be more than the cost of a used engine for your vehicle.
Blue Smoke Coming Out Of Exhaust
If you happen to notice that you are having blue smoke coming out of your exhaust you are likely looking at oil getting into your cylinder walls. If the piston rings of your engine are starting to fail or if you have a leaking valve this can cause oil to get into your engine cylinder and get mixed as part of the combustion process and eventually pushed out of your exhaust in the form of blue smoke.
Blue smoke coming out of your exhaust is going to be common on turbocharged or supercharged engines because of the added stress of the supercharger or turbocharger on the engine. A turbocharger or supercharger compresses the air that is fed to the engine allowing it to get more air into the cylinder wall to be burnt which will increase the power of the engine.
This is good for the overall horsepower ratings of the engine but can add more stress to the different parts of the engine as that compressed air is going to be harder for the engine to handle than normal air flowing from your air intake.
A good illustration of this is the amount of pressure applied to your car’s tires or bicycle tires. The more PSI of air that you have in your tires the more pressure that you will be putting on the sidewall of the tire. If your tires are flat you will likely be able to press down on your tires and they will flex, if you fill your tires to the max amount of PSI advised you likely won’t be able to flex the sidewall of your tires.
The same concept of car tires is applied to your car’s engine as a turbocharger or a supercharger will be forcing more PSI of compressed air into your engine instead of just allowing the air to flow into the cylinder from the atmosphere.
Piston Wear
All of this added stress on the engine can eventually cause the internals of your engine to start to fail or increase the tolerances between the parts of your engine. Your engine’s pistons are designed to be pushed up and down the cylinder walls of your engine block to cause the combustion process.
Over time the thin rings that line the engine’s pistons can start to become worn down which can then cause a gap in between the piston rings and the cylinder walls. When this happens this can allow oil from the crankcase to get pushed up into the cylinder and be burnt with the air and fuel mixture in the cylinder wall. This is one of the main causes of blue smoke coming out of your exhaust.
Bent Valve
Oil getting into the engine’s cylinders can also happen from the top part of your engine as well. Most cars nowadays are going to have overhead cams that are designed to operate the valves of your engine which when open allows air into the cylinder.
The valves then close forcing the air out the exhaust valves. If one of the valves of your engine gets bent this can allow oil from the overhead crank to drip down into the cylinder wall via the valve stem which can cause you to see blue smoke coming out of your exhaust.
Unfortunately, if you have either one of these problems you are likely going to need to tear apart your engine to fix either of these issues. If you have leaking valves you can replace your cylinder head at a somewhat cheap cost of 200 to 300 dollars.
If you need to replace your piston rings you are likely looking at needing to rebuild your engine at that point which can be very expensive depending on what parts you decide to put back into your vehicle’s engine.
If you decide to use the same factory parts that were originally included in your car’s engine it likely won’t be that much to replace them. However, if you plan to use aftermarket forged parts to replace the pistons and rods of your engine you are likely going to be spending a pretty penny to have your engine rebuilt.
Black Smoke Coming Out Of Exhaust
If you are starting to notice that you have black smoke coming out of your exhaust you are likely looking at something to do with your fuel system. The most likely cause of seeing black smoke coming out of your exhaust is that the fuel being pushed through your engine is not being fully burnt off during the combustion process which is why you are seeing it coming out of the exhaust.
Spark Plugs
The first thing that you would want to check if you are seeing black smoke coming out of your exhaust would be the spark plugs of your engine. If your spark plugs are replaced or are all gummed up with carbon deposits they likely won’t be able to fully burn all of the fuel that is in the cylinder during the combustion process. This will allow the excess fuel to be sent out through the exhaust valves and through your catalytic converter.
If you allow unburnt fuel to get sent out of the engine long enough this can eventually cause your catalytic converter to fail as it will eventually be filled up with carbon deposits and not able to filter any of the exhaust gasses coming from your engine. 
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Leaking Fuel Injector
Another common cause of fuel-burning too rich in your engine is going to be a leaking fuel injector. If one of your fuel injectors is cracked or broken that can allow excess fuel to be sent into your engine cylinder.
If you remember if your engine is not able to burn off all of that excess fuel then that is going to cause black smoke to come out of your exhaust. The easiest solution for this would be to replace the leaky fuel injector individually or replace all of your fuel injectors.
If your engine is not able to accurately tell how much air and fuel is being sent into the engine this can also cause all of the fuel from the combustion process to burn. Your engine will use what is called an oxygen sensor or O2 sensor to be able to tell how much air is being sucked into the air intake of your engine.
It can then adjust the engine mapping of your engine and fuel ratio to account for the amount of air coming into your air intake. If your oxygen sensor is not working properly and cannot tell how much air is coming into the air intake this can also cause your engine to run rich as your engine will try to run a rich fuel mixture to try to keep the engine running.
Fuel Pressure Regulator
Another cause of your engine running rich can be an issue with your fuel pressure regulator. If your car’s engine is not able to sense how much fuel pressure it has it will cause your engine to run rich which we now know can cause black smoke to come out of your exhaust.
What can happen over time is that your fuel pressure regulator can get stuck closed which will cause the above-mentioned issues. The fix for this would be to replace your fuel pressure regulator so that your engine can run normally again.
The typical costs for replacing your fuel pressure regulator is going to be anywhere from 150 to 300 dollars for the part and will cost you anywhere from 50 to 300 dollars to be installed by a mechanic.
Smoke Coming Out of Exhaust – In Conclusion
The color the smoke coming out of your exhaust is going to be the main indicator of what type of problem you are having with your vehicle.
If you are seeing white smoke coming out of your exhaust this is usually an issue of coolant getting into your engine cylinders. If you are seeing blue smoke coming out of your exhaust this is usually an issue with oil getting into your engine cylinders. If you are seeing black smoke this is usually an issue of unburnt during the combustion process of your engine.
Hopefully, this article was able to give you some ideas as to what sort of problem you are looking at.