Engine smoking – why is it happening and what should I do next?
Smoke can escape from engines and exhausts with little warning. And depending on the nature of the problem, your car will emit blue, black or white smoke.
If your car is emitting smoke when it’s stationary or accelerating then you shouldn’t ignore the problem. A smoky car may indicate a serious mechanic problem, but this is not always the case.
Here, we run through some of the most common causes behind the a smoky car or van and what you should do to fix it.
My car is smoking – what should I do?
There are numerous reasons why your car could be giving off smoke. Some of the most common causes include:
- leaking head gaskets
- defective coolant systems
- burnt electrical wires
- worn pistons
- faulty fuel valves
To work out what’s causing the smoke, check:
- where the smoke is coming from
- the colour of the smoke
- when the smoke appears
- if your car is overheating
You might find that the clouds aren’t smoke at all, but water vapour condensing on a cold day.
But if you’re sure the smoke is the result of a fault in your car, you should try to identify the problem.
If the smoke appears to be a result of a fire under your bonnet, you should act quickly.
- Turn off your engine
- Pull the bonnet release lever but do not try to prop it open
- Get everyone out of the car and keep your distance
- Dial 999 and ask for the fire service
- Warn oncoming traffic, if it’s safe to do so
The sections below are divided by car parts and the colour of smoke to help you find and fix any faults.
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Different colours of engine smoke and what they all mean
Smoke often leaves car engines as a result of overheating. This can be caused by faulty wire casings, heated residues on the engine block and overheated liquids including oil, transmission fluid and brake fluid.
There may also be a fault in your coolant system, or your engine may not have enough lubricant. No matter the problem, you should find a trusted garage to take a look.
Are you experiencing a car fault, warning, or mechanical problem on your road trip? Find a local mechanic with the RAC.
Black engine smoke
Black smoke leaving your engine is often a sign that too much fuel is being burned. It could also be caused by a clogged air filter. If you catch either fault early, they are usually easy to fix.
1. Faulty fuel injector
Fuel injectors deliver petrol or diesel into the engine as a high-pressure mist. They can become clogged up with dirt or low-quality fuel, or leak because of wear and tear to the seals.
Both the seals and injector itself can be replaced by a qualified mechanic.
2. Damaged fuel pressure regulator
Just as the name suggests, this part of the fuelling system regulates the pressure of petrol and diesel being fed to your car.
The part can be found either outside or inside the fuel tank and this will affect the cost of a replacement.
You should check with your local garage if the fuel pump needs to be replaced at the same time.
3. Dysfunctional carburettor
Older cars use a carburettor to mix air and fuel. When the part fails and delivers too much petrol or diesel to the engine you’ll notice dark smoke.
It’s important to get the problem checked as soon as possible by a professional, as your car will be burning too much fuel and therefore producing excessive emissions.
4. Blocked inlet manifold
The inlet manifold supplies a mixture of fuel and air to cylinders in the engine.
A blocked inlet manifold will only allow a limited amount of the mixture to the combustion system, which can cause your engine to cough up a cloud of dirty smoke.
Although this part can be cleaned at home, it’s best to enlist the help of a professional if you’re not sure what you’re doing.
5. Ignition timing is off
In order to burn properly, fuel must be ignited at the right time during the combustion cycle.
When your ignition timing is off, your engine will burn more fuel than necessary and in extreme cases pump out clouds of black smoke.
If you think your car is using excessive fuel you should have the engine looked at by a trusted mechanic.
White engine smoke
White smoke from your engine is usually a sign that you have a coolant leak. It could be caused by any one of the following problems:
1. Damaged coolant/radiator hoses
Hoses to and from your radiator can collapse, swell and crack over time and you may be able to see the damage for yourself by simply lifting the bonnet.
The parts should be inexpensive to replace and the work is best carried out by a professional.
2. Cracked engine block
Engine blocks hold all the major parts of your engine together.
Extremely low temperatures can lead to coolant freezing and pushing against the walls of the block causing small cracks.
Although uncommon, manufacturing faults can mean some sections of engine blocks may be thinner than others and more vulnerable to damage.
You can try using an engine block sealer for smaller cracks but will need to visit a trusted garage for anything more serious.
A mechanic may need to re-weld parts of the block or use a method known as cold metal stitching to make repairs.
Be warned, the work is very expensive and it could work out cheaper to buy a new car.
Different colours of exhaust smoke and what they all mean
Smoke from the exhaust is usually less serious than smoke leaving the engine.
The colour of the clouds leaving your tailpipe can even help you diagnose the problem elsewhere in your car.
Black exhaust smoke
It’s quite common for cars to give off black smoke from the exhaust when the engine starts up, but if this quickly clears up you should have nothing to worry about.
If the problem persists, your car could be facing one of three problems:
1. Dirty or clogged air filter
Your air filter prevents unwanted debris from being sucked into your car’s engine. Contaminants collect in the filter over time and prevent the filter from working properly. In some cases the filter can also become damaged.
If debris reaches the combustion engine it can be burned along with fuel and escape as black smoke.
Thankfully, a filter replacement is a straightforward job which you can do yourself, or get a garage to do quickly for you.
- 11 ways to reduce your driving emissions
- Glow plug repair and replacement
2. Bad fuel pressure regulator
If your exhaust continues to give off black smoke, your pressure regulator may be faulty. These devices are used to maintain pressure in the fuel system and are usually mounted on the fuel rail.
A faulty regulator can increase pressure in the system and your car’s fuel economy will suffer greatly. In some cases the excess fuel will burn as black smoke.
The RAC Approved Garage network is a great place to search for a professional who can replace the fuel pressure regulator.
3. Leaking or clogged fuel injector
Fuel injectors control the amount of fuel delivered to the combustion chamber. When the parts go bad, you might notice your car shakes when the engine is idle. If the injectors deliver too much fuel, the excess will often burn as black smoke.
It could be a sign that the parts need to be replaced.
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White exhaust smoke
You may notice white smoke leaving your exhaust when you start the engine.
If it quickly disappears, this is usually the result of condensation build up rather than a sign of a more serious problem.
However, if white smoke is visible long after starting your car, your engine is probably burning coolant that has leaked into the combustion chamber. This can happen in three ways:
1. Blown head gasket
The head gasket seals the internal combustion process and keeps coolant and oil from mixing together.
A perforation to your gasket or a blown head gasket usually occurs as a result of an overheated engine. When coolant flows into the combustion chamber from a blown head gasket it burns/evaporates into white smoke.
Check the underside of your oil filler cap. If oil is mixing with water in your engine, there will be a creamy, light-brown deposit on it.
You could try using head gasket sealer to fill out small cracks but more extensive damage will need the help of a professional. Be prepared to pay anything between £500–£1,000 for the repair bill.
- Head gasket guide – why does it fail and how can I tell?
2. Cracked engine block
A cracked engine block is almost impossible to repair. The parts are vital to the running of your car and support a number of key components.
Coolant can leak through the cracks and burn as white smoke from hot points in the engine bay.
You’re better off replacing an engine block entirely, but may want to consider cutting your losses and buying a new car instead.
3. Damaged cylinder heads
Cylinder heads sit on top of the engine block to form the combustion chamber. The parts can become warped through overheating and cause your engine to misfire.
When the air-tight seal is lost, coolant can slip through openings and burn as white smoke.
Because the heads have to fit perfectly with connecting parts, you’ll normally have to replace cylinders rather than repair them.
You can find an RAC Approved Garage to help.
Grey exhaust smoke
A thick grey cloud from your exhaust pipe is usually a sign that your car is burning oil.
Once oil escapes it can burn off as grey smoke from various hot points around the engine.
The liquid can leak into your combustion chamber, leading to reduced fuel economy and eventually, damage to your catalytic converter.
The leaking oil can occur for one of two reasons:
1. Malfunctioning valve stem seal
Valve stem seals lubricate the valve in combustion engines to help maintain the correct ratio of fuel and air. When the parts become loose the seal is lost and oil can leak.
Fixing the problem can be complicated and expensive and you may need to rebuild or replace the engine, so you’ll need a trusted mechanic for the job.
2. Failed piston rings
If bluey-grey smoke leaves your exhaust while your vehicle is accelerating, this is usually the tell-tale sign of damaged piston rings. The parts are found in cylinders and can leak oil when they lose their seal.
The fault is uncommon and will need the help of a professional to fix.
Blue exhaust smoke
Bluey/dark grey smoke is a clear sign that your engine is burning oil. The liquid can leak into the combustion chamber where it is burned along with fuel.
You’ll probably notice your car misfiring when you turn the keys in your ignition, or find your vehicle shakes more than usual when idle.
Since blue and grey smoke coming from your exhaust can point to the same faults, there is naturally a bit of overlap with the above section. These leaks are caused by:
1. Worn pistons and piston rings
Pistons use rings to keep an air tight seal in the cylinders of a combustion engine. After some wear and tear, the rings can leak oil into fuel which eventually burns as blue smoke. Although this usually escapes from the exhaust it can appear from the bonnet too.
Damage to the pistons and piston rings is extremely complicated to fix and we recommend taking your car to an RAC approved garage to make sure repairs are done properly.
2. Damaged valve stem seals
Valves regulate the amount of fuel and air mixture allowed into cylinders for combustion. Although their seals are usually made from high-strength rubber, they can become cracked and worn by extreme temperatures or wear and tear.
Mechanics will often use special tools to compress the valve spring before replacing a valve seal.
3. Malfunctioning PCV valve
A PCV valve or Positive Crankcase Ventilation valve releases exhaust gas and unburned fuel from the engine block.
If the PCV valve gets stuck, it will mix oil, air and other gases inside the engine. The combustion of this mixture will cause blue smoke.
Fixing a PCV valve shouldn’t be too costly and usually involves a replacement rather than a repair job.
4. Worn engine oil seals
As oil travels from the tank around the engine it relies on a number of seals to prevent it from leaking to other areas of the car. These seals can suffer from wear and tear, leading to leaks and oil burning off as blue smoke.
If you notice any blue smoke or oil spillages, visit a trusted garage as soon as possible.
5. Inlet manifold leaks
The inlet manifold supplies a mixture of fuel and air to cylinders in the engine. If the manifold leaks oil into the cylinders, this can burn as blue smoke.
Sealants are available to help patch up small leaks but may only work as a temporary fix. Enlisting the help of a professional is always your best option.
6. Head gasket failure
Head gaskets are responsible for sealing the internal combustion process and can become damaged through overheating, allowing oil into different parts of the engine.
You could try a head gasket sealer to fill out small cracks but be prepared to pay up to £1,000 for more extensive repairs at a garage.
Keep your engine running smoothly
The RAC recommends regular oil changes help keep your engine running smoothly and extend its life. Book an RAC Mobile Mechanic today.
Why Your Car is Smoking Under the Hood and the Burning Smell?
Have you ever noticed smoke coming out from under your car’s hood or smelled something burning while driving? It can be a scary experience, but don’t panic just yet. These are common signs of car trouble that could range from simple issues to more serious problems. Let’s dive into what might be causing the smoke and burning smell, and what you should do about it.
Car Smoking Under the Hood
If you notice smoke coming from your car’s engine, it’s important to address it right away. The smoke might indicate something as simple as an oil leak or something more serious like an overheated engine. Let’s break down some of the most common causes.
Overheated Engine
One of the most common reasons for smoke under the hood is an engine that’s running too hot. If the engine coolant isn’t circulating properly, it can cause the engine to overheat. When the engine temperature gets too high, the coolant may evaporate, producing steam or smoke. Here are a few things that might cause an engine to overheat:
- Low coolant levels
- Leaking or broken radiator hoses
- Faulty thermostat
- A broken water pump
If your engine is overheating, stop driving immediately and let it cool down. Continuing to drive an overheated engine can cause severe damage, leading to expensive repairs.
Oil Leaks
Another common reason for smoke under the hood is oil leaking onto hot engine parts. When oil leaks, it drips onto hot components like the exhaust manifold, which can cause the oil to burn and create smoke. Oil leaks might be caused by:
- Worn-out gaskets or seals
- Cracks in the engine block
- Loose or damaged oil filter
If you spot oil leaking from your engine, it’s crucial to have it fixed as soon as possible. Not only can it cause smoke, but it can also lead to a drop in oil levels, which can damage the engine if left unchecked.
Electrical Issues
Sometimes, smoke under the hood isn’t caused by overheating or oil. It could be the result of an electrical problem, such as a short circuit or overheating wiring. Electrical components can heat up quickly, and if they malfunction, they can emit smoke. Common causes include:
- Faulty wiring or connections
- Malfunctioning alternator
- Burned-out fuses or relays
Electrical issues can be more difficult to diagnose, so it’s always a good idea to have a professional check it out.
What to Do If Your Car Is Smoking
If your car is smoking, don’t panic. Here’s what you should do:
- Pull over to a safe location and turn off the engine.
- Let the engine cool down completely before opening the hood.
- Inspect the engine for signs of leaks or burnt oil.
- Check coolant levels and make sure there’s no obvious damage to hoses or the radiator.
- Call for roadside assistance or have your car towed to a mechanic if needed.
Taking quick action can help prevent further damage and keep you safe.
Burning Smell Coming from Your Car
A burning smell in your car can be alarming, especially if you’re unsure where it’s coming from. Sometimes the smell is harmless, but in other cases, it could indicate a serious issue that requires immediate attention. Let’s explore some of the most common causes of burning smells in your car.
Burning Oil Smell
If you notice a burning oil smell, it’s likely that there’s an oil leak somewhere in the engine. As we mentioned earlier, when oil leaks onto hot engine parts, it burns and creates a strong odor. If you smell burning oil, it’s important to address it quickly because running low on oil can cause serious engine damage.
Common causes of burning oil smells include:
- Leaky oil filter or drain plug
- Worn-out gaskets or seals
- Damaged engine parts
If you’re smelling burning oil, pull over and check your oil levels. If the levels are low, add oil and inspect for any leaks. If you can’t locate the source of the problem, it’s best to take your car to a mechanic.
Burning Rubber Smell
A burning rubber smell can be caused by various issues in your car, and it’s something you should definitely not ignore. The most common cause is a slipping or worn-out serpentine belt. The serpentine belt powers several important components, including the alternator, air conditioning, and power steering. If the belt slips or wears out, it can create friction, which causes the rubber to burn.
Other potential causes of a burning rubber smell include:
- Worn brake pads that are rubbing against the rotor
- Overheated tires that are rubbing against something
- Problems with the transmission or clutch
If you suspect a burning rubber smell, have your serpentine belt, brakes, and tires inspected. Ignoring this smell can lead to further damage or even breakdowns.
Electrical Burning Smell
An electrical burning smell could be a sign that something in your car’s electrical system is overheating or malfunctioning. It could come from a short circuit, a malfunctioning alternator, or faulty wiring. Electrical components in your car generate a lot of heat, and when they fail, they can give off a burning odor.
Here are some signs to watch for:
- Flickering or dimming lights
- Malfunctioning electrical components
- Unusual noises from the alternator or battery
If you smell an electrical burn, it’s best to turn off the car and have it towed to a mechanic for a thorough inspection. Electrical problems can be dangerous and could lead to further damage if left unchecked.
What to Do If You Smell Burning
If you notice a burning smell in your car, here’s what you should do:
- Pull over to a safe location immediately.
- Turn off the engine and allow the car to cool down.
- Check for signs of leaks, burning oil, or damaged belts.
- Inspect your tires and brakes for any unusual wear.
- Have your car towed to a mechanic if necessary.
Ignoring a burning smell can lead to more serious problems and expensive repairs, so it’s best to address the issue sooner rather than later.
How to Prevent Smoking and Burning Smells in Your Car
Now that we’ve covered the main causes of smoking and burning smells in your car, let’s talk about how to prevent these problems from happening in the first place. Regular maintenance is key to keeping your car running smoothly and avoiding costly repairs.
Regular Oil Changes
One of the simplest and most effective ways to prevent smoking and burning oil smells is to keep your engine oil fresh. Old or low oil can cause friction in the engine, leading to overheating, oil leaks, and burning smells. Make sure to change your oil at the recommended intervals (usually every 3,000 to 5,000 miles) to keep your engine running smoothly.
Check Coolant Levels
Low coolant levels can cause your engine to overheat, which can lead to smoke under the hood. Regularly check your coolant levels and top them off as needed. If you notice a sudden drop in coolant, it could indicate a leak, and you should have it checked by a professional.
Inspect Belts and Hoses
Worn-out belts and hoses can cause a variety of problems, including overheating and burning rubber smells. Have your serpentine belt, radiator hoses, and other belts inspected regularly. Replace any worn-out or cracked belts to prevent more serious issues down the road.
Keep an Eye on Your Tires
Tires that are too worn or improperly inflated can cause friction, leading to overheating and burning smells. Check your tire pressure regularly and replace worn-out tires before they become a problem.
Electrical System Maintenance
Your car’s electrical system is essential to its proper functioning. Have your alternator, battery, and wiring checked regularly to avoid electrical issues. If you notice any signs of electrical problems, such as flickering lights or strange smells, get it checked immediately.
I hope this article has helped you understand why your car might be smoking under the hood or why you’re getting that burning smell. Whether it’s a simple issue or something more serious, addressing these problems early can save you time and money. Always stay on top of regular maintenance, and don’t hesitate to seek help from a professional when needed.
Frequently Asked Questions (FAQs)
Is it normal for my car to smoke under the hood?
It’s not normal for your car to smoke under the hood. Smoke often indicates an issue like an overheating engine, oil leak, or electrical problem. If you notice smoke, pull over immediately and have the issue inspected by a mechanic.
Can low coolant cause smoke from my car’s engine?
Yes, low coolant levels can cause your engine to overheat, which may result in smoke coming from under the hood. It’s important to regularly check your coolant levels and address any leaks to avoid engine damage.
Do I need to worry if I smell burning oil in my car?
Yes, a burning oil smell is usually a sign that there is an oil leak or other engine issue. It’s important to investigate the source of the smell right away, as running low on oil can cause severe engine damage.
Is it safe to drive my car if it smells like burning rubber?
If your car smells like burning rubber, it could be due to a worn serpentine belt, damaged brakes, or other issues. It’s best to stop driving and have the car inspected to avoid further damage or a breakdown.
Can a burning smell be a sign of electrical issues in my car?
Yes, a burning smell can indicate electrical problems such as overheating wires or a malfunctioning alternator. Electrical issues should be addressed immediately to prevent further damage or potential fire hazards.
Is it dangerous to drive with a smoking car?
Yes, it can be dangerous to drive with a smoking car. Depending on the cause, you could be risking further engine damage or even a fire. It’s important to pull over safely and investigate the problem or get help from a mechanic.
Can I fix a small oil leak in my car myself?
If you have some mechanical knowledge, you may be able to fix a small oil leak, such as replacing a worn gasket or tightening the oil filter. However, larger leaks or more complex issues should be handled by a professional mechanic.
Do I need to replace my serpentine belt if it smells like burning rubber?
If your serpentine belt is slipping or showing signs of wear, it’s a good idea to replace it. A worn or damaged belt can cause burning rubber smells and may lead to other issues like loss of power steering or air conditioning.
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What Causes a Car Engine to Smoke?
A car engine can smoke for several reasons. If the smoke is blue, it means it’s burning oil. This could be caused by valve stem seals, worn rings, a plugged PCV valve, not changing the oil for extended periods, too high of an oil level or transmission fluid being sucked into the intake manifold from a bad vacuum modulator. When the valve cover is removed, there’s so much sludge built up under the valve covers that it appears like mud.
Over time this mud turn hard like a brick. When the car is started all the oil was going up into the valve cover but with all the sludge it could not get back into the oil pan. All the oil would end up in the valve covers because the holes were blocked up not allowing it to return. When this happens, the oil drains down the valves and into the combustion chamber and it smokes. This is caused by not regularly changing the oil in the car. It will eventually cause an engine to lock up from lack of oil on the crank and bearings.
Black Smoke
If the smoke is black and smells like gas, it could be the spark plugs, the ignition or the wrong mixture in the carburetor (if the car has one) or the same thing in a fuel-injected vehicle with different components. In a fuel-injected vehicle, the map sensor, mass air flow, cam sensor, faulty fuel injector, ECM computer, fuel pressure regulator, bad spark plugs or problem in the ignition circuit could cause black smoke.
White Smoke
If the smoke is white and has no real smell, it’s likely that the head gasket is blown. This is usually caused by overheating the engine and usually causes the oil to be saturated with water. This is particularly bad because the oil is not effective at protecting the bearings and can ruin an engine quickly. It also causes the engine to overheat again because hot gases are getting into the cooling system. White smoke can also come from a leak in the intake manifold runners, allowing water to be mixed with the incoming air.
Don Bowman has been writing for various websites and several online magazines since 2008. He has owned an auto service facility since 1982 and has over 45 years of technical experience as a master ASE tech. Bowman has a business degree from Pennsylvania State University and was an officer in the U.S. Army (aircraft maintenance officer, pilot, six Air Medal awards, two tours Vietnam).
Why Your Car is Smoking Under the Hood and the Burning Smell?
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