My Engine Is Blowing Smoke! What Does It Mean?

My Engine Is Blowing Smoke, What Does It Mean?

So, you put the pedal down and a cloud of smoke can be seen. That’s not good. But what does it mean? Well it depends. Some small amount of smoke may not be a fatal sign in your motor, but too much can be sign things are not well.

Let’s deal with petrol or gasoline type motors and consider some of the symptoms that will help us tell how bad things are.

Firstly how much smoke is your vehicle blowing? When did you notice it?

  •  If you noticed the engine smoke in the rear view mirror. Then it can be a very bad sign. Generally there has to be quite a bit of smoke for you to see it in the rear view mirror! If it wasn’t you that noticed it and someone else has seen it and alerted you, or you saw your own car under heavy acceleration blow some black smoke, it can simply be over rich mixture. This will usually be a puff of dirty black smoke which only really shows up under heavy acceleration. The injectors or carburettor are pushing more fuel into the engine than can be easily burned all at once. This may be no real problem.

What colour is the smoke?

  • If it is blue or blue-white in colour, then it can be another not so good sign. If there is blue in the engine smoke, that means it may be produced from burning oil. Whereas if it is more of a black smoke it may be over rich mixture under heavy acceleration as outlined in the previous point.

 When did you notice the smoking motor?

  • If it is at any time the vehicle is under load or accelerating then this once again may be a not so good sign. If it also seems to get worse as the engine gets hotter. This is also not so good

How is your engine oil holding up?

  • If your oil needs topping up often and there does not seem to be a lot of fresh drips of oil on the ground after parking your car for a while. Then this is a pretty strong indication the oil is going somewhere else than on the ground.

Does the engine seem to be a bit lower in power than it used to be?

  •  If the engine seems to not quite have that same ‘zing’ as it used to, then it could be re-enforcing our oil burning concerns. An oil burning car engine will lose power generally. This can make the car feel sluggish, especially under load. Often this is most noticeable up a decent sort of hill. If it is really feeling like the vehicle is working hard getting up a decent hill, then it is a sign something is not right.

Is the engine running a bit hotter than it used to?

  • If you have a temperature gauge and it seems to have crept up from where it used to be by a few degrees then again this can be a sign we have a tired engine on our hands. Once again this heating will be more pronounced in the up a decent long hill type scenario. If you notice the gauge creeping up as you climb, when you have not noticed it before then this is a sign the motor is not performing well under load.

Is the motor making more noise than it used to under load?

  • Once again, we are on that hill and the motor seems to be clattering, or making more noise than it should every time we push it.  The smoke is there and the rattle is not good.

Does the engine fume when you open the oil filler cap?

  • This can be a good test. But of course it is not wise to do this with a hot engine. If you are not confident to do this step leave it to a professional. Start the engine up and leave it to idle. Loosen the oil filler cap gently. Then remove it completely. If you notice a lot of fumes and pressure coming out of the cap this is also not a good sign. If the fumes look contaminated with smoke too then its a very bad sign. Basically there should be very little ‘fumes’ blowing out of the motor in a motor that is in good condition. There will always be some, but there should not be a lot. Remember to fit the oil cap back in place and clean any spots of oil that may have come out with a rag. Note that the engine may stumble a little bit as you open the cap as the pressure change may affect some controls hooked up to the engine.

 How many miles or kilometres has your engine done?

  •  If you are noticing some of the other signs listed previously and your engine has done a lot of kilometres then this is a big re-enforcer to our diagnosis. If the vehicle has done quite a few hundred thousand kilometres, or a couple of hundred thousand miles. It will surely have wear. If the kilometres are under 100 thousand or under 60 thousand miles and the vehicle has been well serviced; never run out of oil, then it would be very strange for it to have an oil burning issue. If your vehicle has done a lot of work and is showing other signs mentioned then it may be at the end of its life.  It is important to note that you only have to let the engine oil run low once to cause catastrophic damage to the motor.  This hardly seems fair.  But it is the case.

 What will a mechanic do to test and confirm my concerns?

  • A mechanic has a device that can test the compression of a motor or engine. Basically the compression tester goes in one of the spark plug holes and as the motor is cranked by the starter motor it will show the pressure build up in the cylinders. A loss of compression from the standards laid down by the manufacturer for the motor in your vehicle, will tell the mechanic how badly worn things are. This is usually pretty accurate as far as a test of the engine wear goes.

To sum up, let’s say that our engine is blowing blue smoke under acceleration, it does seem sluggish up hills and seems to be getting hot too. When the oil filler cap is removed there are visible fumes blowing out with some pressure. Ok, so now with this set of questions answered we can pretty safely say, we have an oil burning engine on our hands.

Why does the engine or motor smoke?

The engine relies on very precise tolerances between operating parts. It needs oil between all these moving parts too. This avoids the motor seizing or locking up due to friction. But you can imagine that if over time, due to wear, the gaps between these parts gets a bit too wide we can get an issue where oil ends up where it should not be in large quantity. Such as in the combustion chamber. You can imagine that if we put oil on a fire we are going to get smoke! So what happens is the oil in a worn motor is allowed to pass by things like valves and piston rings. This allows it to get into the combustion chamber and with each firing of the fuel air mix the excess oil gets turned to smoke. The harder you work the motor the worse this gets. It can often be called bypass. Not only does the oil bypass the seals, but also the pressurised gas. This also means that the pressure can flow back into the crank case and up into the rocker covers. If you did the check of removing the oil filler cap. Then you may have seen those fumes. The ones that bypass the sealing engine parts such as the valves and pistons.

The two illustrations below show in very simple graphic terms where the oil and pressure bypass the worn parts.

Oil Bypasses Worn Rings And Valve Stem Seals

Oil In The Engine By-Passes Seals And Piston Rings
Oil In The Engine By-Passes Seals And Piston Rings

Hot Gasses Bypass Worn Valve Stem Seals And Rings

Hot gasses bypassing worn rings and valve stem seals
Hot Gasses Bypassing Worn Rings And Valve Stem Seals


What can I do about this problem?

It is possible through diagnosis to find that the valve stems are worn according to the graphic but the piston rings seem ok.  Or vice versa. Some mechanics may advise getting the head reconditioned as a cost effective option. This can be a very short term fix. What can happen is that the reconditioned head which now has the full seal back pushes the pressure right up to where it should be. But due to the bottom end and rings not being put back to standards, the extra pressure now starts to bypass the old rings. Even if it was not doing that before. This is due to the old rings not really bypassing that much under the low pressure of the worn and tired valves keeping the pressure extra low. So often what happens if one part of the motor is re-built is that the other will fail due to the extra pressures being placed on it by the reconditioned parts. The best options are to either recondition all parts of the motor. Or alternatively get a replacement used engine that has plenty of miles/kilometres left on the clock.  Here is a great place to buy used engines with plenty of miles left on the clock.

Anything short of these two solutions will usually come back as another problem in the near future. Please also see the section on fitting a replacement engine for other useful tips about the cooling system etc.

Having tried many short cuts over the years, I can vouch for how much money I have wasted not doing the job correctly from the start. If the motor is showing that it is an oil burner then it is really a terminal engine and is needing to be replaced or given an extensive reconditioning.

Why not just keep driving?

Well often you can for a while. But remember the EPA (Environmental Protection Authority) or RTA (Road Traffic Authority) may think otherwise. In many states, it is encouraged to report offenders. So it is probably only a matter of time before you get caught and end up with a fine.

Beside the penalty for being a polluter there is also the issue of pollution to the environment at a real and moral level. The more people that make sure they have an engine in good working condition in their vehicles, the less pollution we have. This will help us all minimise damage to our shared air quality and cut the detrimental effects to human health. So consider all these things when you are working out what to do with your old smokey.

If you put a replacement power plant in, you will often feel the joy of driving a fully powered vehicle again. Often we don’t realise how much power the old work horse has lost. With a freshly replaced well performing engine, driving can become a joy again. Not to mention avoiding having to stop constantly and check that fast diminishing oil level!

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