If there is one sign that even the most oblivious of owners will recognise as signifying their vehicle is in trouble, it is smoke belching from the exhaust.
This smoke can materialise in different colours – black, blue, grey and white – and while the different colours indicate different ailments and problems, none of them can be ignored. Unfortunately, most of the causes of smoke can be catastrophic to a car’s health if they aren’t tackled quickly, so it’s important that an inspection and diagnosis be performed by a qualified mechanic as soon as the issue becomes obvious and persistent. Early detection and repair can spare you a much more substantial repair bill down the track.
So, what do each of the different smoke colours mean?
BLACK SMOKE
Amongst other things, an engine’s performance relies on the correct ratio of fuel and air being injected, and then consumed, in the combustion chambers. Black smoke indicates this ratio is off and that there is too much fuel in the mix. Components that could be at fault here include the fuel injection system, which is responsible for introducing fuel into the chambers, to a clogged air filter that may be impeding the smooth flow of air.
BLUE SMOKE
Blue smoke is a tell-tale sign that oil has leaked into the engine’s combustion chamber and is being burned along with the fuel and air mixture. The cause of the leak could be degraded piston rings or valve seals within the engine. It could even mean that the head gasket – the component that seals the gap between the engine block and cylinder heads – is damaged, and that can lead to calamitous engine failure.
While an oil leak in the engine is the most likely cause of blue smoke, there are other potential culprits. Included amongst these is the turbocharger which, like the engine itself, uses oil for lubrication of its parts. A turbocharger’s job is to force more air into the cylinders which allows for more fuel to be burnt and more power produced. However, if there is an oil leak, the turbo can end up blowing that oil into the engine’s combustion chambers. The result? Blue smoke.
GREY SMOKE
Thick grey smoke can be caused by a couple of different issues. It can be an indication, like blue smoke, that the car is burning oil, but it is more likely a sign that transmission fluid is being burned. This fluid is used to lubricate components in the transmission system while also acting as a coolant. Any fall in its volume will result in a loss of lubrication and can cause significant damage to the transmission system. It’s tough to drive a car without gears!
WHITE SMOKE
Billowing white smoke from the exhaust is a sign that the vehicle’s engine coolant is leaking and being burned. This is a serious problem as it could mean that the head gasket has failed, that there is a damaged cylinder head or even that the engine block is cracked – all of which can lead to fatal engine damage.
It should be noted that there is often some white vapour expelled from the exhaust when an engine is first started. This vapour is likely the result of condensation in the exhaust system. It is the thick, persistent, white smoke that is of major concern,
Whatever the cause, there is no good reason to ignore exhaust smoke, and all types and colours are a sign of a problem that needs to be addressed. Doing so early, when the symptoms first appear, can make a potentially difficult and expensive repair job a lot more straightforward for the mechanic and a lot less expensive for the owner.
WANT TO LEARN MORE?
MTA Queensland’s Vehicle Maintenance course is designed for those who are interested in gaining valuable information and learning good practices for everyday vehicle use. The result: a safer journey with fewer breakdowns and repairs. If you have ever wanted to learn how to carry out preventative maintenance, then this course is for you.
5 December 2019
Please note the information contained on this page is general in nature and does not take into account your specific needs or circumstances. You should consider whether the information is appropriate to your needs, and where appropriate, seek professional advice.