Why is white smoke coming from my exhaust?
White smoke or steam/water vapour escaping from the exhaust of a vehicle can be a sign that water from the cooling system is mixing with the oil and moving into the engine, which is one of the most noticeable symptoms of a blown head gasket.
How is steam from the exhaust caused by a blown head gasket?
The head gasket sits inside the engine and is a very important component in keeping the engine oil and engine coolant separate, so that the oil can lubricate all of the working components of the engine and the coolant can manage the temperature of the engine, each from their own respective circulation channels.
When a head gasket is blown, the seal between the two systems is broken, allowing water to enter the areas of the engine where it should not be; the oil channels and combustion chamber.
This means the water is exposed to much higher temperatures than it would be in the cooling system water has a much lower state transition temperature than oil which results in water vapour or steam escaping the exhaust system. This is why white smoke is often reported by owners of vehicles which are subsequently diagnosed with a blown head gasket.
Why should I fix my blown head gasket?
The most likely reason for water vapour exiting the exhaust and therefore water entering the combustion chamber is a blown head gasket, which brings other symptoms with it which can eventually result in a complete lack of compression in the engine, causing the vehicle to become a non-starter. But there are other reasons why you should not have water in your engine, too.
Loss of coolant
Due to the pressure inside an engine, once a head gasket is blown the water is pushed into the oil channels and combustion chamber, where the heat of the engine causes it to evaporate and be ejected as steam. This means that water is being moved out of the cooling system and then out of the vehicle completely, resulting in significant coolant loss.
The loss of coolant means that the engine temperature is no longer managed by the cooling system, as there is less or no water/antifreeze to maintain an equilibrium. This increases the chances of the engine overheating, which is dangerous and unhealthy for the engine.
Damage to other engine components
When an engine overheats it operates at higher temperatures than it safely should, creating a fire hazard and potentially warping other components within the engine, which is one of the reasons why the mechanical repair of a blown head gasket is so expensive. Not only does the engine have to be dismantled so that the head gasket can be replaced, but the cylinder heads also have to be skimmed to remove any imperfections caused by operating under strenuous conditions.
My exhaust emits white smoke/steam: What should I do?
If you have noticed steam, white smoke or water vapour escaping from the exhaust, take your vehicle to a mechanic to diagnose the problem. If white smoke is escaping from the bonnet, do not drive the vehicle, and immediately research your repair options.