Nobody ever wants to see smoke coming out of their car’s tailpipe. In most cases, some thin white smoke from your exhaust in the winter is perfectly normal and generally not a source of concern.
However, whenever you notice thick bursts of white smoke coming from the exhaust, this is a sign that something is wrong with various components of your engine, whether it’s white smoke from exhaust on startup or white smoke from the exhaust when accelerating.
This article will provide you will all the different reasons why your exhaust may be producing white smoke and ways to fix it!
Table of Contents
- What’s a Normal Exhaust Emission?
- What Does White Smoke From Exhaust Mean?
- Petrol Engines vs Diesel Engines: White Smoke From Exhaust
- Reasons Why There is White Smoke Coming Out of Exhaust
- Troubleshooting and Fixing White Smoke From Exhaust
- FAQs (Frequently Asked Questions)
What’s a Normal Exhaust Emission?
Before we dive into why white smoke from the exhaust when accelerating is an issue, let’s first discuss what a normal exhaust emission should be like!
A spark ignites the mixture of fuel and air inside an engine’s combustion chamber, which then creates a series of combustions, or contained explosions, inside the cylinder.
As a result of these explosions, a direct byproduct is exhaust gases that are then funnelled down the exhaust system. Before exiting through your exhaust pipe, these gasses pass through the muffler and a catalytic converter to reduce noise and harmful emissions respectively.
Under normal conditions, if everything is working as it should, you should not be able to see the exhaust smoke coming out of your exhaust pipe.
In winter, however, you might occasionally see a thin veil of exhaust smoke that is white in colour, which is generally just water vapour. This is absolutely normal and will disappear after a very short period.
It’s crucial to be aware that while thin white smoke from the exhaust is standard if the smoke is thick and comes out in noticeable bursts, you will need to conduct an inspection of various components to identify the source of the issue. Which we will discuss in detail within this article!
What Does White Smoke From Exhaust Mean?
If your exhaust is emitting hick white smoke then this suggests that coolant or water has somehow found its way into the combustion chamber, which it should ideally never do.
When this coolant or water is burned within the combustion chamber, it will begin to produce a thick white smoke that will exit through your exhaust system.
White smoke emitting through the exhaust in thick bursts is quite a common problem, and you should never ignore it and allow it to prolong.
But why is their smoke coming from exhaust? Some of the most common reasons include cracks and damages to vital engine parts, such as the cylinder head, head gasket or engine blocks.
It doesn’t matter if it’s only a tiny crack, the damage can easily become worse as you continue to drive the vehicle and postpone trying to fix the cracked component.
What could happen? Worst case scenario involves further contamination of engine oil or the engine overheating, which can ultimately lead to permanent engine damage – expensive right? You’d then have to replace the completely broken down engine, which is money I’m sure we’d all prefer not to have to spend.
Petrol Engines vs Diesel Engines: White Smoke From Exhaust
If you encounter white smoke from the exhaust, it’s important to understand that this means different sources of problems in gas-powered and diesel-powered engines.
When you encounter white smoke in your diesel-powered car, it typically means that the fuel is not burning correctly due to a lack of heat in the combustion chamber. This unburnt diesel does not only cause white smoke but also contains certain toxins that will be more than likely to sting your eyes.
If you own a diesel-powered vehicle, in addition to the reasons that will be discussed below, white smoke from the exhaust is usually caused by:
- low cylinder compression
- low fuel pressure to the fuel pump
- damaged fuel lines
- incorrect or broken fuel pump timing
- broken injection timing
- cracked or damaged rings or cylinder liners
- broken crankshaft keyway
| Engine Type | Diagnosis | Possible Causes |
|---|---|---|
| Petrol Engine | Incomplete air/fuel mixture | • Faulty fuel injection system • Incorrect fuel injection and valve timing • Engine overheating • Faulty fuel pump and/or injection pump |
| Diesel Engine | Leaking coolant or water dripping into combustion chamber | • Bad head gasket • Cracked block or cylinder head |
Reasons Why There is White Smoke Coming Out of Exhaust
Time to dig into the reasons why there is white smoke from exhaust on startup in detail, to help you better understand what might be happening with your vehicle. The most common reasons:
- Piston ring or valve seal leak
- Condensation
- Damaged coolant reservoir tank
- Cracks in the cylinder head, head gasket or engine block
- Failing fuel injectors
- Engine control unit error
- Incorrect injector pump timing (diesel engines)
Piston Ring or Valve Leak
It’s sometimes possible for the white smoke coming from the exhaust to be tinted blue, although it can often be hard to notice this. This blue-tinted white smoke is an indication that your engine is burning oil.
Inside a combustion chamber should be a clear-cut mixture of air and fuel. If oil were to somehow find its way into the cylinder it will be ignited together with this air and fuel mixture.
Due to this burning oil, you will witness a thick blue-ish cloud of smoke exiting the exhaust pipe. Though, as I said, it might appear to be white smoke to a lot of people as it can be hard to distinguish. Other signs to look out for are engine misfiring and increasing oil consumption.
The big question here is how can oil leak into the combustion chamber? This is most likely due to faulty/leaky piston rings or valve seals, which therefore are allowing oil to flow inside of the combustion chamber.
Other resulting issues to this problem are that when oil is leaking, the engine components are therefore not being lubricated properly, which leads to them starting to wear prematurely.
This will cause a whole additional herd of costly repairs and replacements that no vehicle owner would want to deal with.
In most cases, you shouldn’t have to deal with leaky piston rings or valve seals until after the 100,000-mile mark. One way to help prolong their lifespan is to switch to high-mileage motor oil.
Condensation
A sign of condensation build-up within the exhaust system is when there is thin white smoke on startup that then disappears. This tends to occur during the winter months or cold mornings. This isn’t an alarming problem!
The smoke in this instance will be thin, not too visible and only be coming out in small amounts upon startup. After around 30 seconds to about a minute, the white smoke should dissipate.
As I said, it is not a sign of trouble, but if it occurs in concurrence with other occurrences of reduced engine performance or difficult starting, it may indicate a more serious issue within your engine that will need to be addressed immediately.
Damaged Coolant Reservoir Tank
If the coolant reservoir tank becomes damaged or cracked, it’s possible that it may leak coolant into the combustion chamber of the engine. This leaking coolant then burns within the cylinders, resulting in a cloud of thick white smoke exiting the exhaust.
A cracked coolant reservoir tank leak is generally not as bad as the sources of leaks that follow. However, please be careful if you’re fixing other problems near the tank to not accidentally damage the coolant reservoir tank.
In any case, where the coolant tank becomes damaged, you will need to replace the reservoir tank.
Cracks in the Cylinder Head, Head Gasket or Engine Block
A cracked coolant reservoir tank is not the most common of issues, and when mechanics hear about thick white smoke from the exhaust of a vehicle, they will instantly assume the worst.
The worst? A crack in the cylinder head, head gasket or engine block, all of which are lengthy and costly to replace.
Cracks in these components of the engine are typically caused by a consistently overheating engine. This is likely to be due to low coolant levels, which is because of the leaking coolant, and constant temperature fluctuations of the engine.
These cracks allow for coolant or oil to leak into the cylinders, which then becomes burned and produces thick white smoke from the exhaust.
Cracked Cylinder Head
If your cylinder head is cracked or damaged in any form of way, coolant will leak out of it and get mixed up with the engine oil. This leads to the contamination of the oil.
All it takes is a tiny crack, not even a big one, to create thick bursts of white smoke from your exhaust pipe. As the coolant leak continues to mix in with engine oil, the white smoke will begin to have a distinct sweet odour that will not go away so easily.
Cracked Head Gasket
A head gasket is a thin metal sheet found between the cylinder head and the engine block, sandwiching the top and bottom parts of most engines. Head gaskets are designed to form a seal between the two parts and help to prevent coolant leaks from the cover surrounding the engine.
Head gaskets may undergo cracks due to normal wear and tear. The coolant is no longer contained within the cooling channels of the engine when this occurs and instead finds its way into the cylinder, where it will burn.
A cracked head gasket, unfortunately, cannot be repaired, and so, will need to be replaced immediately.
Cracked Engine Block
Now, the absolute worst-case scenario is that your entire engine block has a crack in it. If this is the problem, then you should prepare yourself for a very expensive and time-consuming replacement.
The majority of engine blocks are made out of either aluminium or cast-iron alloy so that they are able to last longer in constant high-heat conditions, along with being able to effectively transfer heat away from the engine.
However, the engine is a very complex system that requires each and every component to work with absolute precision and no room for error. If any of the engine components aren’t working as they should, the block itself will overheat, which will naturally weaken and deteriorate it.
There are few common symptoms that will indicate the block is getting too hot other than the white smoke coming from the exhaust. These include:
- discoloured coolant
- puddles of fluid under your car
- frozen coolant in the radiator
- poor performance of the engine since it cannot maintain proper compression if there’s a leak in the combustion chamber.
Failing Fuel Injectors
A fuel injector’s role is to deliver fuel to the combustion chamber as input for the combustions, acting as a spray nozzle. Many people think the injector can control when or how much fuel gets sent into the chamber, but it doesn’t. A fuel injector acts only to restrict or allow fuel.
For combustion within the engine’s chamber to be at its optimum, the fuel must be injected at precise moments, meaning that even the slightest variation can throw the system off balance.
If the fuel injector were to leak or get stuck in the open position, or malfunction in any type of way, then the oil chamber is no longer working at its optimum and receiving the correct amount of fuel at the right time.
If there becomes too much fuel in the engine that needs to burn off and be expelled, the result is thick white smoke from the exhaust, which may sometimes be a tinted grey-like colour. If this is happening, then it is possible that your fuel injectors have become clogged, which will make them effectively useless.
It’s not generally not advised to inspect the injection or try to change it yourself, as it is a job best left up to the professionals. One of the main reasons that fuel injectors fail is because of contaminants in the fuel. A way to try to avoid this is by replacing the fuel filter routinely.
Engine Control Unit Error
Leading on from the last point, it’s possible that you might have a faulty engine control unit that is throwing off the timing of the fuel injector. This simply means you must reset or repair the engine control unit so that it can correct the timing of the fuel pump injector.
To reprogram the computer, it may be as simple as unplugging your car battery for a few minutes. Otherwise, you may need to take your car to a certified mechanic who is familiar with the engine of your vehicle’s make and model.
Incorrect Injector Pump Timing (Diesel Engines)
Well, if your engine runs on diesel, the reason for white smoke from the exhaust pipe is most likely an issue with the injector pump timing. This pump is in charge of injecting diesel into the cylinders.
Just as with the fuel injector in a gas-powered engine, if the pump’s timing is off and diesel is not delivered to the engine’s chamber at the required precise moments, it can lead to an overrun of diesel, causing thick white smoke to come out of the exhaust pipe.
Other signs of injector pump failure on a diesel engine include difficulty on startup, poor idling, reduced performance, reduced RPM limit and poor fuel economy.
Troubleshooting and Fixing White Smoke From Exhaust
When it comes to troubleshooting steps you can take to try and fix, and stop, the white smoke coming out of the exhaust, there are a number of steps you can take.
Inspect Valve Seals or Piston Rings
Valve seals and piston rings are prone to wear and tear. If they fail, a replacement is in order. Unfortunately, unless you fancy yourself a self-taught DIY mechanic and are very knowledgeable about dismantling an entire engine, it’s recommended that you leave this to the professionals.
Though the parts might sound simple, replacing piston rings can be extremely expensive, usually ranging from £1,000 to £2,500, of which the parts only cost around £50-£150. The remaining costs are for the ever-so time-consuming labour.
Replacing valve seals costs a tad less than piston rings, but I would still expect it to cost you from £500 to as high as £1,500. Similar to piston rings replacement, the process of replacing valve seals involves disassembling the entire engine until you can reach the valve spring, costing a lot in labour.
Check Coolant Level
If you’re still unsure whether you have a coolant leak and want further proof that you’re having an issue with coolant making its way into your engine block, you should first check the coolant level.
If you observe that the level is lower than it should be and do not see coolant leaking from the coolant reservoir tank, this will suggest that the leak is due to a crack in the head gasket, cylinder head or engine block.
Furthermore, it is generally advised that you invest in an engine block leak detector kit that will utilise chemistry to detect whether your coolant is contaminated or not.
The first step here would be to open the hood. Then you can open the coolant reservoir and look into the coolant chamber to check the coolant level.
Look for the markings on the side of the plastic overflow bottle that says “Low” and “Full,” or any similar terms, before grabbing a funnel and filling the reservoir until the level reaches “Full”. One alternative way is to put a stick into its reservoir and check how much coolant is in there.
If the amount of coolant is at an adequate level, you can proceed to inspect the other engine components below for any cracks or potential damage that might lead to the coolant getting mixed with engine oil or fuel.
It’s also advisable that you perform a cooling system pressure check to try to determine which part is actually causing the leak. To do so:
- Pressure is initially applied to the system up to the range specified on the cap of the radiator.
- If the system cannot hold pressure for at least two minutes, then there’s going to be a leak somewhere.
- If no external leaks are found, the likeliest possibility is a crack in the head gasket, cylinder head or engine block.
Note: don’t forget that the engine should be sufficiently cool before you remove the radiator cap or reservoir cap. If the engine is hot, give it at least an hour or longer to cool down before you attempt to check the coolant.
Look For Cracks
Look For Cracks In The Intake Manifold Gasket
The first thing to inspect is the intake manifold gasket. The intake gasket seals the intake manifold, and not only transports coolant to the engine but also oxygen.
If the intake gasket were to develop a crack, the engine will overheat due to leaking coolant, air, and gas. The gasket is prone to damage caused by extreme heat because it is mostly made of rubber or plastic.
Although it can get cracked or damaged, fortunately, it can easily be repaired if it is detected early. The replacement cost of an intake manifold gasket is anywhere from £100 to £400.
The gasket itself is relatively cheap and will cost somewhere between £10 to £100. What’s expensive, once again, is the cost of labour, which will be anywhere from £100 to £300.
Look For Cracks In The Head Gasket
The next component is to inspect for cracks in the head gasket. The head gasket is designed to prevent the coolant from getting to the cylinder by providing a seal from the head to the block. If there’s a crack in the head gasket, it will need to be replaced immediately.
The cost of head gasket repairs is likely to run into the thousands, meaning it’s often easier and cheaper to just scrap the damaged part and replace it.
It generally costs between £1,000 and £2,000 to replace a head gasket. The cost for the parts themselves varies between £500 and £750, while the labour costs range from £600 to £1,000.
Look For Cracks In The Cylinder Head
The cylinder head is essential in connecting to the engine block and head gasket. Due to the fact that it’s made of aluminium, It’s prone to warping or breaking in the case of engine overheating as it is made of aluminium, which releases white smoke from the exhaust.
If you spot a crack upon inspection, you should replace the cylinder head right away. Cracks in cast iron heads can often be repaired by either furnace welding or flame spray welding.
If the crack cannot be repaired, however, the entire cylinder-head will need to be replaced. This can be an extremely time-consuming job, regardless of whether it is easy or not because the engine head will need to be removed and then replaced, thus a large portion of the replacement cost is labour cost.
Note: labour costs will vary greatly depending on the make and model of your vehicle. Luxury vehicles like BMWs, and Audis often have various components that need to be removed to get to the cylinder heads, hence leading to lengthier jobs and additional costs.
The average cost for cylinder head replacement is between £2,000 and £3,000. While labour costs are estimated between £1,000 and £2,500 with parts costing only from £100 to £400.
Look For Cracks In The Engine Block
To repair a cracked engine block you typically have three possibilities; using a cold-metal patch over the crack, cold-metal stitching it shut or re-welding the crack. Each of these methods will require the work of a professional.
Regardless of which route you opt for, it, unfortunately, will not be cheap. Depending on the make and model of your vehicle, it could take anything up to around 35 hours of labour for the engine block to be repaired.
This is because for some luxury models it’ll be much harder to get to the engine block and disassemble it. This can set you off between £2,000-£4,000 for only a temporary fix.
It may be more sensible to salvage your current engine and get an engine block replacement. If this is the case then you can expect to pay between £500 and £1,000 for small block engines or between £1,000 and £2,500 for a long block engine, of course, dependent on the model being swapped.
Don’t forget the labour cost! This alone for a typical engine block replacement can run anywhere from £500 to £2,000.
Clear or Replace the Fuel Injector
It’s possible that your fuel injectors are clogged and are unable to do their job effectively. This part is generally susceptible to getting clogged by carbon deposits, sludge formation, and other contaminants.
Some good news is that there are commercial fuel injector cleaners that can help clear a dirty fuel injector with ease. Otherwise, if the fuel injector is failing and it’s not because of clogs, it has probably reached the end of its life, and so, you must replace it.
Note: you should always replace the entire set of fuel injectors rather than just replacing the problematic one, or else the engine may not run evenly.
Diesel Engine Fuel Pump Replacement
If reprogramming the computer because the timing of the injector pump is off doesn’t solve the issue, you will most likely have to replace the pump entirely.
The average cost for a fuel pump replacement may be between £150 and £1,000 depending on the vehicle make and model. The other possibility is that you have to replace the camshaft, which can run between £1,000 – £3,000.
These jobs are not suitable for the novice and will require professional help, as it requires tools and knowledge that only a certified mechanic would have.
After you have the replacement performed, try to avoid contaminants in the diesel causing additional fuel injector pump failure. I would advise routinely replacing the diesel fuel filter, in addition to buying the highest quality of diesel you can afford in-store or at the gas station.
FAQs (Frequently Asked Questions)
To fix white smoke coming from your exhaust, I would first check the coolant level, before inspecting the piston rings and valve seals for signs of leakage. Look for cracks in the intake manifold gasket, head gasket, cylinder head, and engine block. Finally, clear or replace the fuel injector.
White smoke coming out of your exhaust is likely due to a coolant leak, but it doesn’t always mean your head gasket is blown. It could be an issue with the coolant reservoir tanks itself, or cracks in the intake manifold gasket, cylinder head, or engine block.
You certainly shouldn’t. It’s best to diagnose what the problem is with your vehicle. If for instance you have a gasket failure or a crack in a component, and you continue to drive, this further contamination or overheating of the engine block may result in your engine completely breaking down and needing an expensive replacement.
Please comment below if you have any questions regarding white smoke coming from the exhaust when accelerating!
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