Exhaust Smoke

The sight of ‘smoke’ billowing from your exhaust may cause you to think the worst. However, before you start to panic it is worth considering a few things first, as there are a few different types and causes of exhaust smoke and it may simply be harmless condensation. Of course, we do recommend having a professional to look at any smoking from the exhaust, as some of the causes may be potentially serious for your vehicle.

In fact, you can often gauge the potential sources of the problem and it’s severity by looking at the type of smoke produced.


If you start your vehicle, especially on a cold day and see white smoke from the tailpipe then you are likely just seeing condensation, or steam. If this disappears once the vehicle has warmed up, then this is almost certainly the cause and it is perfectly normal and nothing to worry about.

If after the vehicle has warmed up, and particularly under acceleration the smoke continues then it is time for further investigation as there is likely a more serious issue and could even be a symptom of a blown head gasket.

The white smoke, which is really steam, is a sign that there may be coolant leaking into combustion chambers where it gets burned off creating the steam. This is a common symptom of a blown head gasket or cracked block and immediate attention is required. If this is the case then you may be faced with a huge repair bill and this is where a sealer such as Steel Seal can help and possibly save you thousands.

One further point to note is that white smoke can also be caused in diesel motors through a fault in the fuel injection system, often referred to as ‘running rich’. In this instance not all fuel is burned during the usual engine processes and it is expelled through the exhaust as white smoke.


When visible, blue smoke may indicate that oil is mixing with fuel, often as a result of worn gaskets or seals. An external oil leak may also present as blue smoke as it is burned off when contacting a hot engine. If the oil is overfilled this may also occur, so be sure to check that your oil is always filled to the correct level for your vehicle.

An engine is a complicated system with many gaskets and seals, and there are several which could be at fault to cause this, the worst of which would be the head gasket itself. If a blown head gasket is suspected as the result of an oil leak please speak to our technical team before attempting to use Steel Seal, as it will not be effective for external oil leaks, rather only when the damage can be reached through the cooling system. We want you to have the best chance of success, and sometimes that includes not using our product at all if it simply isn’t going to help.

We would always recommend seeking an immediate diagnosis from a professional mechanic if you notice blue exhaust smoke.


The presence of grey smoke may indicate several things, from a faulty turbo, a problem with the Positive Crankcase Ventilation (PCV), the job of which is to reduce vehicle emissions, or simply oil burn off. We would always recommend having your vehicle looked at straight away if you see grey smoke.

One further reason that you may see grey smoke from the exhaust could be a transmission system leak that may occur in automatic vehicles. The smoke will be produced as transmission fluid is drawn back into the engine and burned up. Again, it is recommended to seek immediate advice from a qualified mechanic.


The presence of black exhaust smoke may indicate an imbalance in the mix of fuel added during combustion. The engine burns too much fuel, and this is seen as black smoke, which is a mixture of soot deposits and other particulates. You will certainly notice that your vehicle’s fuel consumption suffers as a result, as well as the environment, so it is well worth getting checked out straight away.

Again, there are several possible causes for this, some of which include a clogged air filter, faulty EGR valve, blocked manifold, faulty sensor or a fault with the fuel injection system.

Your Diesel Particulate Filter (DPF) may also be the cause if you drive a diesel vehicle. This is designed to burn off excess sooty deposits when the vehicle is driven, usually when it reaches freeway speeds of around 70mph. This is not something to worry about if it happens intermittently when driving at these speeds, but if you only drive short distances on a regular basis or rarely reach freeway speeds then you may develop problem with the DPF, often indicated by a DPF warning light.

In all of the above cases, if you are worried by the presence of of exhaust smoke we always recommend speaking to a qualified, reputable mechanic for a correct diagnosis. Our technical team are also always at hand if you need some help, and if the worst happens and a blown head gasket is the culprit, we are there to advise on the use of Steel Seal, and hopefully get you back on the road as quickly as possible.