Is It Normal For Diesel Engines To Smoke When Cold?

While starting a diesel engine, a plume of white smoke is most evident, especially when it’s cold.

This is because colder air is denser than warm air, therefore temperatures in engine cylinders at the end of the compression stroke are lower. Because of the cooler air, the fuel fed into the cylinders burns more slowly. The unburned fuel droplets are ejected as a cloud of white smoke.

Is white smoke on diesel cold start normal?

“White smoke is an indicator of unburned diesel fuel,” says Zack Ellison of Cummins. It usually happens during startup in cold weather when engines have decreased compression and delayed timing. During startup, you have an incomplete combustion, which allows raw diesel fuel to stream out of the stack.”

White smoke typically dissipates rapidly. “When you start the engine at idle speed, at 650 or 700 rpm, you obtain a better compression ratio. “It gets pretty hot very rapidly,” Ellison observes. “You are more susceptible to white smoke if you have an older engine with low compression, improper timing, or low injection pressure.”

White smoke can also be caused by a low cetane grade. “You could have some problems with white smoke if the fuel has a low cetane rating,” adds Ellison, “since the diesel fuel doesn’t ignite as rapidly when you inject it.”

“Excessive oil use almost always results in blue smoke,” says Ben Hanks of John Deere Power Systems.

A high fuel-to-air ratio results in black smoke. Either the fuel pump has been turned up or the air intake/exhaust system has a limitation. “You could have a clogged intake, lowering your air/fuel ratio,” Ellison explains. “The black smoke is just more fuel fed into the engine than the engine can burn.

Another possibility is a lack of upkeep. “There is likely to be significant black smoke if the air cleaner is not properly maintained,” Hanks explains.

*This essay was first published in 2011, and it was updated in 2020.

Why does my diesel car smoke when I start it?

Have you observed smoke pouring out of the exhaust pipe of your diesel vehicle? Perhaps you notice smoke when starting the automobile, especially in cold weather, or when accelerating.

If any of these things are happening to your car right now, it’s most likely a sign that something is wrong with it. In most cases, there should be no visible smoke coming from a diesel car’s exhaust.

Causes of white smoke

Raw diesel flowing out of a car’s exhaust before it has been thoroughly burned can produce white smoke. This could be due to defective fuel injectors in the engine or poor cylinder compression. The latter issue could be caused by a fault with the engine’s valves, piston rings, or cylinders.

If white smoke develops in the exhaust of your diesel automobile while the vehicle is idling during a cold start (starting the engine at room temperature) and then disappears as the vehicle accelerates and the engine warms up, there may be a problem with the piston rings or cylinders.

Water can enter combustion areas through broken head gaskets or damaged cylinder blocks, resulting in white smoke.

How to prevent it

If you use a flush cleaner on the engine to lessen the dirtiness of essential components, you should be able to eliminate white smoke from being released during cold starts. This product should be available at auto repair shops.

If this doesn’t stop the white smoke from appearing and you suspect a problem with engine components, you should take your diesel automobile to a competent garage. In this case, be prepared to pay for repairs.

Causes of blue smoke

Because oil is being burned, blue smoke may be released during a cold start when the automobile is idle. It’s possible that this is due to a problem with the engine oil. It’s possible that the oil used in the car is the wrong quality for the engine, meaning it’s too thick or thin to effectively run the engine.

Alternatively, oil may be consumed as a result of a fault with one or more engine components, such as valve guides or seals, piston rings, or cylinders.

Using a flush cleaner on your diesel car’s engine, similar to how you stop white smoke from being emitted, could be just what you need to reduce blue smoke emissions.

If blue smoke continues to come out after you’ve applied this, you may have a more significant engine problem that you should have checked out at a mechanic.

Causes of black smoke

Black smoke is the most prevalent sort of smoke that may be seen coming from a diesel car’s exhaust system. It’s frequently a sign of insufficient and or incomplete diesel fuel combustion.

There are a number of possible causes, including filthy or worn fuel injectors, a defective turbocharger, worn or stuck piston rings, a dirty air filter, or the engine operating at a lower-than-normal temperature.

Black smoke can also be generated if you overfuel or use a low-quality fuel.

Make sure you get good fuel from reputable sources and that your air filter isn’t too dirty on a regular basis. These are two good strategies to limit the possibilities of your diesel car emitting black smoke in the future, or to put a stop to it if it has already happened.

Engine components may need to be cleaned to their original state from time to time, which you may perform with a flush cleaner on the engine. It’s pretty simple to replace the air filter if it’s dirty.

If black smoke persists despite taking all of these steps, it’s most likely due to other engine components. In that situation, hiring a professional to evaluate the engine and make any necessary adjustments is a good idea.

Is it normal for diesel engines to smoke?

Even though black smoke from a diesel engine is frequent, some individuals are nevertheless concerned. As a result, we’re frequently asked what black smoke from a diesel engine means. It shows that the engine has a problem and, in most cases, implies an uneven fuel/air ratio or a more complex issue. Normally, diesel engines should not produce much smoke when operating; nonetheless, certain older diesels are known to emit smoke when accelerating under load.

How do I stop my diesel from smoking?

Diesel engines are known for being filthy and producing a lot of black smoke. One of the most common images is of a diesel rig speeding down the highway, black smoke billowing from the stacks. That was pretty much viewed as normal in the 1960s, 1970s, and 1980s. All of this is unfortunate, because a diesel engine is more efficient and reliable than a gasoline engine.

The modern common-rail diesel engines are a significant improvement over older diesel engines, allowing for significant increases in horsepower and performance without producing a lot of black smoke.

The corollary to this is that if your diesel emits black smoke, it means something is wrong and needs to be corrected.

Not only does it make you look ugly, but it’s also bad for the environment, and it’ll cost you more in the long run because black smoke implies lower fuel mileage and more money out of your wallet. So, let’s look at what produces black smoke in diesel engines to see how we might lessen it.

Restricted Air

Fuel that hasn’t completely burned is seen as black smoke. When a diesel engine is working properly, it will totally burn the fuel, producing CO2 and water. As a result, black smoke indicates that something is preventing the fuel from totally burning. The appropriate amount of air is required to completely burn the fuel, which is a vital component of the combustion process. Incomplete fuel combustion results from a lack of air.

What may be the source of this suffocating air? It could be due to a clogged or limited air cleaner system.

Turbocharger Lag = Puffs of Black Smoke

When large diesels with huge loads are about to accelerate from a standstill, they often puff black smoke. This enormous diesel has massive turbochargers that require a long time and a lot of fuel to get up and running “Spool it up.” They’ll do this while they’re waiting for the ball to start rolling “Before the light turns green, they “roll coal,” trying to get the turbocharger up to speed before they move. This consumes a lot of gasoline in an engine that runs at low RPMs.

This problem occurs primarily in older trucks and is a design flaw. There isn’t much that can be done about it besides perhaps adding a combustion catalyst to the fuel to increase the amount of diesel burned at low RPMs.

Incorrect fuel/air ratio or injector problems

Black smoke is produced when a mechanical issue breaks the equilibrium between the proper quantity of fuel and the right amount of air being burned. It could be as simple as tweaking the injector timing or inspecting the EGR system to ensure the EGR valve does not require replacement.

If it’s not like that, you’re dealing with a mechanical issue. It’s possible that the valve clearances are incorrect. Alternatively, the injectors may need to be examined. The most critical component of a well-running diesel engine is the fuel injectors. You won’t receive the finest atomization of the fuel if they’re worn or plugged, which is what the engine relies on for its optimal performance.

Engine Deposits Will Cause Black Smoke

When a car is brand new, it performs at its best. Engine conditions deteriorate over time, resulting in accumulations of combustion product combustion in important regions such as injectors and combustion chambers. And all of this gets in the way of optimal performance.

Diesel engines are particularly susceptible to this since a) they operate for such a long time and b) diesel fuel does not arrive from the refinery with any detergent packets already added.

The solution is to regularly add a detergent component to your diesel fuel. Dee-Zol is a multipurpose treatment that cleans up deposits, reduces the quantity of fuel consumed inefficiently, and can even extend the life of your DPF (because less soot are being produced at any one time).

What does GREY smoke from a diesel mean?

Simply put, when it comes to grey smoke, diesel cars release it when there isn’t enough oil in the tank. Aside from indicating that your diesel engine is using too much oil, the smoke could also indicate: A malfunctioning PCV valve (Positive Crankcase Ventilation) – This component is in charge of emission control.

What color should diesel smoke be?

On startup, a brand new diesel engine running at full load will experience some blow-by. Blow-by occurs when diesel fuel, air, or vapor is pushed past the rings and into the engine’s crankcase. In order for proper combustion to take place, the cylinder chamber must be kept at the right pressure. The rings in a new diesel engine need time to seat properly and form an airtight seal. The blow-by problem should go away after a few hours of break-in time under load. As a result, a properly operating diesel engine should emit no visible smoke from the exhaust system. If there is smoke coming from the exhaust, it could be a sign of a more serious engine problem. This article will assist you in determining the root causes of diesel engine smoke.

White, black, and blue are the three colors of diesel engine smoke. Smoke flowing from the exhaust pipe on a regular basis most likely signifies a more serious internal engine problem. Due to a lag before the turbocharger’s air flow can meet the increased volume of diesel fuel delivered into the cylinders, a little puff of smoke during rapid acceleration is normal with earlier diesel engines. Newer electronic diesel engines with common rail injectors synchronize the turbo’s speed to the metered flow of diesel fuel into the cylinder at the same time.

White Smoke:

The injectors are frequently the source of white smoke emanating from the exhaust system. White smoke usually indicates that the diesel fuel isn’t burning properly. Unburned diesel fuel will pass totally unnoticed through the exhaust system. White smoke should be avoided since it irritates the eyes and skin. When white smoke appears during a cold start and then disappears, it’s likely due to frozen deposits of soot that grew around the rings and then burned away as the engine warmed up. It is recommended that glow plugs be used during cold starts and/or that a flushing solution be used to eliminate engine muck.

Black Smoke:

In contrast to white smoke, black smoke has a high concentration of carbon exhaust particles. The lengthy chain of carbon molecules in diesel fuel is broken down into smaller and smaller molecular chains when it burns in the cylinders. The result of the exhaust leaving the engines is a mixture of carbon dioxide and water. If something goes wrong during combustion, the chemical reaction is not as strong, resulting in long tail hydrocarbons remaining intact and being ejected as smog or soot. When diesel fuel is partially burned, huge carbon dioxide particles and greenhouse gases are released, contributing to air pollution. The introduction of the Selective Catalytic Converter, Diesel Exhaust Fluid, and Diesel Particulate Filter all helped to regenerate exhaust back into the combustion chamber, allowing particulate matter to be broken down even more.

Black smoke is the most prevalent color of smoke produced by a diesel engine, and it indicates that something is wrong with the diesel fuel combustion process. The blend of air and fuel flow into the cylinders is the first place to investigate when diagnosing the problem. There could be too much gasoline, too enough fuel, too much air, or simply not enough air being delivered by the engine.

Blue Smoke:

Blue engine smoke is the most uncommon sort of smoke produced by a diesel engine. The presence of blue smoke indicates that oil is being burned. Blue smoke is not to be dismissed, although it is usual when starting a car in cold weather. When the oil is cold, it thins out, and some may escape into the cylinder and be burned. Due to deposits present around the rings or cylinders, cold temperatures can cause older, more worn rings to dislodge a little. Cylinder glaze, or the smooth deposits left behind as the piston rises and falls, can also accumulate and burn with time. After the initial break-in time, the seal between the combustion chamber and the crankcase should be entirely sealed. Using Lubriplate 105 or Molybdenum Disulfide during the engine rebuild will help the rings seat properly and burn off any carbon deposits upon restart.

Common Causes of Blue Smoke:

It is not something you should overlook, regardless of the color of the smoke. There should be no visible smoke from a properly operating and maintained diesel engine. If you notice significant smoke, make sure to turn off the engine right once, as any additional heat or load could badly harm the engine.

How do I stop my diesel from black smoke?

If you want to eliminate black smoke from your diesel engine, the first thing you should do is check the air filter and replace it if it’s unclean.

The presence of black smoke in the combustion chamber indicates that the fuel is only partially burnt. Water and CO2 are produced when a working diesel engine consumes the fuel. Black smoke indicates that something is stopping the fuel from completely burning, which is usually due to an unbalanced air-fuel ratio.

The air mixture entering the combustion chamber is the first place to look. The engine air filter, which may be clogged, is the most straightforward repair. The air-fuel ratio will run rich if there isn’t enough air getting to the engine, leaving unburned diesel fuel behind.

What causes GREY smoke from exhaust?

  • Excess oil, a PCV valve failure, or a transmission fluid leak in automatic autos can all cause grey smoke from the exhaust.
  • In a petrol car, black smoke from the exhaust indicates that too much fuel is being burned and could indicate a problem with the air filter or fuel injectors. It’s more likely to be soot buildup or the diesel particulate filter cleaning itself in diesel autos. A lengthy drive, preferably on a highway to allow for higher speeds and revs, should allow the filter to clean itself, eliminating the issue.

Can turbo cause white smoke?

Hi! The most common symptom of a leaking turbo is white smoke coming from the exhaust. The white smoke is usually caused by the turbo spilling oil internally, although it can also be caused by internal coolant leakage. Because there will most likely be a lot of buildup, the turbo may need to be cleaned, reinstalled, and inspected again to pinpoint the source of the leak. Valve leakage is another common source of white smoke coming from the exhaust system. I would also recommend checking the engine’s compression ratio when checking the valves. Any further internal engine leakage that may be present will be revealed by the compression test. To make sure this is the case, have a skilled technician look at the smoke you’re describing and inspect the inside of the turbo for leaks.

How much smoke is normal for a diesel?

There are various explanations for black smoke, often known as “rolling coal,” that you should investigate. Let’s look at some of the most prevalent sources of black smoke and how to deal with them.

Causes of Black Smoke From Exhaust

On a perfectly operating diesel, a little black smoke is typical; in fact, some diesel owners increase the injector size to generate more black smoke. However, it’s a good idea to keep a watch on the amount of black smoke produced at various RPMs and loads to see if anything is wrong.

Incorrect timing or air/fuel ratio, filthy injectors or common rail injectors that stay open too long, a damaged turbocharger, a dirty intake manifold or clogged air cleaner, low cylinder compression, poor quality fuel, or excessive carbon buildup in the combustion chamber are all possible causes.

How To Stop Black Diesel Exhaust Smoke

When it comes to getting rid of black exhaust smoke, the Stiction Eliminator is a wonderful place to start. It will clean and lubricate the turbo internals, the camshaft, and the HEUI injectors. It can aid in the restoration of compression, ensuring that the combustion chamber performs at its best.

In other cases, a shot of Diesel Extreme could be just what you need to clear out those clogged injectors and get them blazing like new. It’s also a great way to clean the fuel system while increasing performance.

You might also replace your air filter, inspect the intake manifold, or fiddle with your aftermarket tuner. If you don’t have much expertise with these types of replacements, see a specialist. Keep in mind that running rich (having too much fuel) is always preferable to running lean (having insufficient fuel). A lean air/fuel ratio can destroy an engine quickly and is often the source of black smoke from a diesel engine.