Why does my Diesel car produce white exhaust smoke?

Hello Paul, my 2016 diesel Toyota Land Cruiser Prado produces a lot of white smoke from the exhaust, which stops after a while. It will then repeat the same behaviour. I have changed the diesel filter but it still does the same. Kindly advise. Kenneth

Hello Kenneth, the common causes of white smoke in the exhaust of a diesel engine are coolant leakage into the combustion system and, occasionally, delivery of excessive raw diesel fuel which cannot be amply burnt by the combustion system. When coolant leaks into an engine combustion system, it cannot be completely burnt just as the fuel. So, it will be expelled through the exhaust as white smoke.

Coolant leaks into the engine combustion system when the cylinder head gasket fails. This is a sealing material fitted between the engine block and cylinder head to ensure that coolant and oil do not cross flow as the fluids move around the engine. When the cylinder head gasket fails, it may allow coolant to leak into the combustion chamber or mix with engine oil. Occasionally, a crack in the engine block can cause coolant to leak into the combustion chamber.

Excessive unburnt diesel fuel can infiltrate the combustion system when your engine fuel injectors are faulty and leak more diesel than the system can amply burn at any given time. The resultant unburnt fuel is expelled through the exhaust as white or black smoke.

A good mechanic will be able to investigate and determine which of the two factors is causing the white smoke. Frequent need to top up engine coolant, mixing of coolant with engine oil (oil colour changes to milky brown) can be a signs of coolant leak into an engine.

On the other hand, excessive diesel fuel consumption, hard starts and poor performance can be signs of leaking fuel injectors.