Blue Smoke from the Exhaust (Causes and Solutions)
Have you ever noticed how your car pulls off at a traffic light and leaves a huge cloud of foul-smelling blue smoke in its wake? Maybe this is your car. You may be wondering why this happens.
A cloud of blue smoke usually means one thing: oil is burning. Instead of just filling up the oil pan and continuing to drive, consider the effects of your engine burning too much oil. Is blue smoke a bad sign?
Yes, blue smoke is generally a bad sign. Not only is it harmful to the environment, but it can also be an early warning sign that you’ll need a costly repair, such as an engine overhaul.
Common causes of blue smoke from the exhaust
1) Bad valve cover gasket
Valve cover gaskets (also known as cam gaskets or rocker arm gaskets) are usually cheap and easy to repair, but they often leak over time. A leak inside the valve cover gasket can allow oil to get into the combustion chamber through the spark plug holes. If this is the cause, you should see oil in the spark plug wells, covering the spark plug tips as well. This could be on one or more cylinders.
2) Bad valve guide seals
Valve guide seals (also called valve seals) are the seals around the valve stem of each valve. These seals can wear over time.
A leaking valve guide seal can allow engine oil to leak from the head, through the valves, and into the combustion chamber. This oil burns with the rest of the mixture, causing blue smoke.
If you notice more blue smoke when braking, it could be that your guide seals are bad. This is because the engine’s vacuum is more likely to draw oil into the engine when it’s under load than when it is under load.
3) Worn piston rings
When it comes to blue smoke, the first thing that comes to mind for many people is worn piston rings. If you notice more blue smoke at high revs, it could be that your piston rings are bad. One piston has three rings: an oil ring, a compression ring, and a wiper ring.
Not sure which piston ring is the problem? A compression test can help you figure out the overall condition of your engine and which cylinder in particular is causing the oil burn.
When doing a compression test, look for relatively similar numbers across all cylinders. If any cylinders show compression values that are too low, you should consider an engine overhaul. Low compression not only causes oil loss, but also loss of power.
4) Faulty PCV valve
A faulty PCV valve can allow excess oil into the intake manifold. This oil gets sucked into the combustion chamber and burns with the rest of the mixture.
Faulty PCV valves are usually cheap, easy to obtain, and easy to replace. One way to test the valve is to shake it. If you hear a rattle, the valve is likely fine. A defective valve will make little to no noise.
You can also try installing the PCV valve in the intake manifold and running the engine without the valve cover installed. If you place your finger on the cut-off end, you should feel a slight suction from the vacuum in the intake manifold.
If you no longer feel any intake or the engine starts sputtering, you may need a new PCV valve. My smoke isn’t blue. What does it mean? White smoke
Excessive white smoke is a telltale sign that your coolant is burning. You may notice white smoke, especially during startup or when you press the accelerator to rev the engine.
A leaking head gasket or defective intake manifold gasket can allow coolant to get into the combustion chamber. Sometimes the engine may overheat as well.
If you suspect that your head gasket is leaking, you can perform a leak test. This test will show if air is somehow able to get from the combustion chamber into the cooling system. This test is performed once per cylinder while each cylinder is on its compression stroke.
Black Smoke
Diesel engines, in particular, can produce black smoke if they are not operating properly. Black smoke is soot produced by incomplete combustion. It usually occurs when the air/fuel mixture is too rich.
It could also be a problem with the exhaust system, such as a dirty EGR valve.
Gasoline engines can also produce black smoke, but this tends to be slightly less noticeable than a poorly running diesel engine. A gasoline engine running rich does not necessarily produce smoke. However, you may notice a fuel smell coming from the exhaust.
How much does it cost to repair?
The cost of a blue smoke repair depends on the problem affecting your car. A PCV valve can be replaced for about $10 and is often easily available. A simple valve cover replacement should only cost you about $200 for parts and labor. An engine rebuild can cost around $4,000, depending on the engine and parts replaced.
When dealing with this issue, it’s very important to find a mechanic who can make the correct diagnosis the first time.