Engine Repair

Causes of White Smoke from the Exhaust

Aaron Coates's image for:
"Causes of White Smoke from the Exhaust"
Image by: 

Any time there is white smoke coming out of your car's exhaust system, it is an indication of a leak. This is not just any kind of leak, but a leak that is allowing either oil, coolant, or transmission fluid to get into the cylinders. The smoke is from the leaking substance not getting completely burned off like the air and fuel mixture does under normal operating conditions. In order to understand what is causing white smoke to come out of your car's exhaust pipes, you should become familiar with the different ways that these chemicals can enter the cylinders. Sometimes an engine that lets white smoke out of the exhaust system is completely normal because of condensation in the exhaust system being burned off.

Starting with the engine oil it should be common sense as to how it can be allowed to enter the combustion chambers in your engine, since oil is what lubricates all of the parts inside your engine. When oil burns, it leaves kind of a blue tint to the smoke, but it looks white to most people. After a few years of use, the rings that seal the pistons in your engine do not seal as good as they used to. There are scraper rings that are supposed to wipe the oil off the cylinder walls, and they get worn out also. When these rings wear out, there is a film of oil that stays on the cylinder wall, and when the combustion process happens, that oil gets burned away and is sent out the exhaust pipe along with the burnt air and fuel mixture. That is one way that oil enters the cylinders and cause white looking smoke to come out of the exhaust pipes. If this is the case, the engine will smoke the whole time it is running, and the exhaust will smell like burning oil. The only way to correct this situation is to re-seal the cylinders with new rings, which usually means a rebuild or an entire engine replacement.

One of the most basic ways this can happen is also very inexpensive to fix, and is completely normal. If the PCV valve is old it can leak and oil can be allowed to suck through the valve into the intake manifold. That is why you should change the PCV valve in your engine at least once a year if it needs it or not.

Another way that oil is allowed to enter the cylinders to be burned is through the valves. The valves in your engine go through machined surfaces that are called valve guides. These valve guides can also wear out, and let oil leak through them. That is the reason why there are seals on the top of the valves, to stop oil from dripping down the valve stem, and entering the cylinders where it can be burned. Worn valve guides can be replaced without rebuilding the entire engine, and if they are not that worn, you can get away with simply removing the valve spring and putting new seals on the valve stems. If the valve guides are worn too badly, however, the entire cylinder head will need to be removed from the engine, and rebuilt at a machine shop. When an engine smokes because of valve guide problems, it will only smoke for a few minutes after the engine is first started, and then it will stop smoking. 

If the coolant in your engine is being burned in the cylinders and causing white smoke to come out of the exhaust pipes, you will know right away, because the smell is very different from oil. Coolant smells "sweet" when it burns, and can be evidence of a major engine problem. More times than not, white smoke that is caused by coolant entering the cylinders is an indication of more damage than if it were oil that was being burned off. The only way coolant can enter a cylinder is through a leak in the water jacket in your engine. A leaking water jacket is usually an indication of a crack in a cylinder wall, a head casting, or (if you are lucky) a leaking head gasket. Besides the only obvious fix for a cracked engine casting is to replace it, even if it is only a head gasket that is leaking there can still be major problems inside the engine because coolant does not compress when it is in a cylinder. Since the coolant does not compress, when the piston comes up on the compression stroke, it can actually bend the connecting rod that connects the piston to the crankshaft in the bottom of the engine. So if you have white smoke coming from the exhaust of your car, and it has a sweet smell to it, you might have a very expensive repair bill in the near future that requires complete replacement of the engine, and not just rebuilding it. 

Another common cause of white smoke coming from the exhaust of your car's exhaust pipes really only applies to older vehicles with automatic transmissions and something called a modulator valve. The modulator valve hooks to the intake manifold on the engine, and the suction from the engine helps your transmission know when to shift. When a modulator valve gets worn out, it begins to leak and let some of the transmission fluid get sucked into the intake manifold to be burned in the cylinders with the rest of the air that goes through the intake manifold. Burning transmission fluid does not really have any kind of smell, you will see a lot of very thick white smoke though. Even though transmission fluid is actually good for cleaning out the inside of your engine, and will not damage it, you will need to address the situation very quickly because the engine can actually suck all of the fluid out of your transmission, leaving you with another very expensive repair bill for replacing the transmission. 

The last common cause for white smoke to come out of the exhaust pipes on your car's engine is normal condensation. After a cool night, when you crank the engine the dew that collects on your grass also collects in the exhaust pipes on your car. Since the exhaust system heats up very quickly, the moisture also evaporates quickly, and can create some steam. This is completely  normal, and there is no cause for alarm when this happens. About the only way you can prevent this from happening is to park your car in a climate controlled garage. 

Okay, now you are familiar with some of the common causes of white smoke coming out of an engine's exhaust system, and hopefully you can figure out how to find the cause. If not, then looking at the spark plugs, checking vacuum hoses, and fluid levels will help you narrow down the part of the system that is leaking. Once you know what system is having the problem, you can use the process of elimination from the causes introduced in this article to find and fix the problem. Thanks for reading.

More about this author: Aaron Coates

From Around the Web