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Exhaust Smoke… What the colour tells us.

When we carry out a car inspection one thing we look for is excessive smoke. Why you might ask?? Keep reading we will give you the basics behind whats actually going on in your engine and why it is important to closely check what comes out the exhaust.


Blue Smoke

Car Inspection

If your car is blowing blue smoke, it’s a clear sign that the engine is burning oil. What happens is that the valve stem seals or piston rings are worn , and oil is leaking past from where it should be lubricating the moving parts, to the combustion chamber where it’s being burned up with the fuel.

If you’re seeing this kind of smoke, check your oil regularly and watch for consumption issues. While an issue that normally should require immediate attention and expensive repairs, including some internal replacement parts, if your vehicle is old and the leak is minimal, it can be carefully managed by topping up the oil on a regular basis.

Along with environmental damage, burning oil can cause rough starts, wear to engine due to low oil and fowl up the spark plugs causing engine performance problems.

There is another reason for blue smoke, and that’s if the car is turbocharged; the smoke being a sign that the blower is in need of rebuilding or replacement.




White Smoke

Car Inspection

White smoke can be nothing to be concerned about if it’s thin, like vapor. This is probably the result of normal condensation buildup inside the exhaust system. This kind of smoke disappears quickly.

However, thicker smoke is a big problem, and can be caused the engine burning coolant. This can be the result of a serious issue like a blown head gasket, a damaged cylinder head, or a cracked engine block – all of which are very expensive repairs.

Don’t ignore it, however, as the problem could become far worse. Even a small leak in the coolant can lead to overheating and serious risk of damage to the engine. A coolant leak can also mix with oil and cause serious headaches for you and your car.




Grey Smoke

Car Inspection

Grey smoke is hard to diagnose directly. Like blue smoke, it can mean that the car is burning oil or suffering from a bad turbocharger. Take the same precautions as with blue smoke, and check for excessive oil consumption.


Furthermore, gray smoke could mean a stuck PCV Valve The PCV system (Positive Crankcase Ventilation) cuts down on harmful emissions by recycling them back into the combustion chamber. However, when the PCV valve gets stuck, pressure can build and lead to oil leaks. PCV Valves aren’t expensive, and can be a quick job for a mechanic or a do-it-yourselfer.







Black Smoke

Car Inspection

Black exhaust smoke means the engine is burning too much fuel. The first thing you should check is ensure your air filter is not blocked or dirty. Following that AFM, Injectors and fuel pressure regulator could also be the culprit. Other reasons could be a clogged fuel return line. Black smoke is usually the easiest issue to diagnose and fix, but burning unnecessary fuel will definitely affect your fuel economy, so don’t think of avoiding this one to save money, it won’t work.








Remember to always check what comes out the exhaust and if you have any concerns take it to your local garage for an emissions check and inspection.