What causes blue exhaust smoke?
By Bardahl • The 8/24/2021 • 5 min reading
It is not always easy to see an abnormal amount of smoke coming from the exhaust of your vehicle. But since blue smoke often corresponds to burnt oil, you can smell it. You can also see it in your rearview mirror when accelerating.
Beyond the particular smell that this burnt oil can give off, it should above all alert you to a mechanical problem: in fact, it means that oil is escaping into the combustion chamber of your engine, leading to excess oil consumption that you should watch out for.
The main causes
A joint or segmentation problem
If oil ends up in the combustion chamber, there are several possible explanations: either the piston rings are worn and letting oil through, or the valve stem seals no longer provide the necessary seal. In both cases, it is simply a question of wear. The valve stem seals can possibly be replaced, but it is more complex – and much more expensive – to consider replacing the segment.
If it is a question of worn segment, the compression ratio may decrease, leading to a slight drop in engine power.
To improve the situation without repair, you can try to increase the viscosity grade of your engine oil or use the following products*:
- Rebalances and increases compressions.
- Improves power, responsiveness and acceleration.
- Strengthens the oil film.
- Protects against cold start wear.
- Stops oil leaks and seepage.
- Reduces oil consumption.
- Reduces engine noise.
- Does not clog the oil filter.
- Stops and permanently prevents leaks and seepage.
- Restores the original properties of O-rings (rubber, neoprene) and sealing rings.
- Acts on internal and external engine seals.
- Does not clog the oil filter.
- Strengthens the hot viscosity index.
- Reduces friction between moving parts.
- Restores compressions.
- Restores power and nervousness.
- Reduces engine wear and noise.
- Reduces oil consumption and smoke emissions.
Turbo failure
A turbo that is not running optimally can also leak oil from the intake side or directly from the exhaust. This can happen if the turbo's oil return line is clogged or when the oil pressure (or level) is too high.
Turbo cleaner
- Removes soot and carbon deposits that cause variable geometry turbos to seize.
- Cleans the moving blades, variable geometry and turbo fins without disassembly.
- Reduces fouling of the turbo, EGR valve, particulate filter, exhaust and catalytic converter.
- Reduces seizure and improves turbo performance.
- Limits excess fuel consumption and pollutant emissions.
- Increases engine efficiency through better diffusion of exhaust gases.
- Extends turbo life.
A clogged breather pipe
If your vehicle is equipped with a breather, over time and with the kilometers traveled, it can eventually become clogged. Its role is to filter residual oil vapors before returning them to the intake circuit. If the breather no longer fulfills its role properly, the oil vapors return to the combustion chamber via the intake, without being filtered enough, which can cause this famous blue smoke.
If you suspect a problem with the breather, consult your mechanic.
Less common causes
Oil circuit
If a break appears in the oil circuit, whether on the cylinder head gasket side or elsewhere, it is possible that oil will also infiltrate the combustion chamber.
Injectors or spark plugs
Although blue smoke is most often caused by oil, it is also possible that unburned fuel is leaking in quantity. If this is the case, you should notice it with an abnormal increase in fuel consumption, due to a problem with injectors (clogged) or spark plugs (which trigger the combustion of the air-fuel mixture) on a gasoline engine.
Diesel injector cleaner
Fuel injector cleaner
- Cleans and protects the entire injection system.
- Restores injector flow.
- Eliminates holes in acceleration and unstable idling.
- Avoids excess fuel consumption.
- Limits pollutant emissions from the exhaust.
*Preferably, ask your garage for advice and they will carry out a diagnosis.