What Causes White Smoke from Diesel Engines?

Billowing white smoke exiting your diesel exhaust can be a nerve-wracking sight, and there are several reasons it could happen. In this blog post, we’ll share common causes of white smoke from a diesel exhaust, how to diagnose the issue and, most importantly, how to prevent it from happening again. 

What Causes White Smoke from a Diesel Engine? 

White smoke from a diesel engine usually means unburned fuel, coolant or oil is entering the combustion chamber. Let’s dive a bit deeper.

Faulty Fuel Injectors 

Faulty fuel injectors are common culprits behind a diesel blowing white smoke and are often the first thing a diesel technician inspects. To help you understand why, we'll explain how diesel engines work. Diesel engine cylinders contain combustion chambers that follow a four-stroke process to power the diesel vehicle:  

1. Inlet valves open to let fresh air in that forces the pistons down. 
2. As the pistons return upward, the inlet valves close, and the air compresses, raising the temperature and pressure in the chamber. 
3. The fuel injector introduces an atomized version of fuel to the pressurized air, causing a spontaneous combustion that burns the fuel. The high-energy fluid then forces the pistons back downward, and the fluid energy converts to mechanical energy. 
4. Inertia in the combustion chamber drives the piston back up. Exhaust valves open and expel any remaining burnt fuel. 

As you can see, the fuel injector must release the right amount of fuel at the right time. If it doesn't, raw diesel may sneak through the combustion chamber and back out of the exhaust stream, causing white smoke.  

Coolant Leak 

When coolant leaks into the combustion chamber, it will escape through the exhaust with the burnt fuel, causing white smoke and sometimes a sweet smell. 

When it comes to coolant leaks, cracked head gaskets are common offenders. The head gasket sits between the cylinder head (a component above the cylinders that houses intake and exhaust valves) and the engine block (the structure that houses the cylinders). 

It serves as an airtight seal between the two components and helps circulate coolant from the top to the bottom of the engine. If the head gasket cracks along a coolant path, fluid can leak into the cylinder and into the combustion chamber, where it will escape through the exhaust and cause white smoke. 

Coolant can also leak into the internal part of the engine through a cracked cylinder head or engine block. Despite this reason, you should visit a repair shop as soon as possible. Coolant leaks can cause the engine to overheat.  

Oil Issues 

Oil leaks can also cause white smoke from a diesel exhaust. Oil can sneak into the combustion chamber through damaged parts like valve seals, piston rings and gaskets. As you might've guessed, the oil will exit through the exhaust and cause white smoke. 

But the white smoke is the least of your worries. Oil lubricates moving parts to maintain a smooth performance. If the leak isn’t addressed in time, important engine parts will deteriorate, causing larger issues. 

Diagnosing White Smoke from Diesel Engine

Visual Inspection 

Before panicking, examine the white smoke. If it’s thick and billowing, it’s time to pop the hood or get your vehicle to a repair shop. If it looks more like steam than smoke and it’s cold out, it’s likely from frozen soot burning away. When compared to the causes above, this is a minor issue. Checking and replacing your glow plugs might help.   

Check Coolant Levels 

Checking your coolant levels at home is simple. Turn off your vehicle and allow the engine to cool down for one to three hours. Once that time has passed, pop the hood and locate the coolant reservoir. Coolant fluid is typically green, pink, red, yellow or blue and in a clear plastic reservoir. 

The reservoir will have a maximum and minimum line on it. If the coolant is nearing the minimum line or beneath it, you may have a coolant leak. 

As mentioned above coolant is typically a translucent green, pink, red, yellow or blue color. If it looks rusted or oily in texture, it’s likely been contaminated from a leak in a major component. At this point, the eye of a trained diesel mechanic can help you determine where the leak is. 

Compression Test 

A compression engine test can also reveal the cause of diesel engine white smoke. It exposes internal issues, like a damaged head gasket, cylinder or valve. Technicians perform diesel engine compression tests when a vehicle has performance issues, such as loss of acceleration or poor fuel economy. 

During a compression test, the technician will place a gauge on each cylinder to calculate how much pressure is being produced. If a cylinder is underperforming, they’ll begin searching for internal damage. 

Examine Oil Condition 

If you’ve ruled everything else out, it may be time to pull the dipstick and check the condition of your oil. To check your oil, turn your car off and pop the hood. Grab a cloth and then locate the dipstick. Most dipsticks are on the left side of the engine and have an orange or yellow handle.  

Once you locate the dipstick, pull it out and use your cloth to wipe away the excess oil. Reinsert the dipstick, pushing it down as far as possible. Pull it out once more and look at the labeled lines toward the bottom of the stick. Most of them say “add” and “safe”. 

If there’s oil between the two lines, you’re in the clear. If it’s at or below the add line, you’re low on oil and should get the vehicle checked out by a diesel mechanic. 

How to Prevent White Smoke from Diesel Engine 

Regular Maintenance 

Taking your diesel vehicle in for routine preventative maintenance and the 30,000-, 60,000- and 90,000-mile services may prevent white smoke from diesel engines and extend their life. During maintenance, technicians inspect and test the systems and components that can cause issues like white smoke. They also change your oil per the manufacturer’s specs. 

Monitor Coolant Levels 

Make a habit of checking your engine coolant every 30,000 to 80,000 miles. As mentioned above, checking it is simple and could save you a later headache. 

Adhere to the Original Equipment Manufacturer’s Oil Specs 

Frequently using the incorrect oil can deteriorate engine seals, allowing oil to sneak into the combustion chamber, where it can cause damage and burn faster. Stick with the original equipment manufacturer’s recommendations to keep important engine components running at optimal conditions. 

Address Issues Promptly 

Engines are complex machines with several interdependent parts. To put it plainly, if you notice something's off – time is of the essence. Seeking the help of a trained diesel mechanic as soon as possible may spare you the dread that accompanies seeing white smoke through your rearview mirror.  

FAQs  

How do you fix white smoke from a diesel engine? 

Depending on the cause of the white smoke, a diesel technician may perform a leak search and repair, replace an internal engine part like the fuel injector or head gasket or address engine oil issues. 

Does white smoke mean a blown engine? 

No, the term “blown engine” refers to an engine with catastrophic mechanical damage to multiple internal parts. White smoke rarely indicates a permanently damaged vehicle. Still, if not assessed promptly, costly damage could occur. 

Can you drive with white smoke from diesel exhaust?  

White smoke from a diesel engine when accelerating may be evidence of a serious issue in the engine. If you experience this, don’t continue driving the vehicle. Get it to a diesel repair mechanic as soon as possible.  

Learn More at Universal Technical Institute 

White smoke from diesel exhausts can indicate several things, including a faulty fuel injector, coolant leak, cracked internal seal or oil issue. Whatever the cause may be, addressing it as soon as possible can prevent costly repairs and be crucial to the longevity of your vehicle. 

Want to learn more about diagnosing, repairing and maintaining diesel engines? Request information to learn about Universal Technical Institute’s diesel mechanic school,¹ offered at campuses nationwide, including: 

• Long Beach, California.
• Rancho Cucamonga, California.
• Sacramento, California.
• Avondale, Arizona.
• Austin, Texas.
• Dallas/Fort Worth, Texas.
• Houston, Texas.
• Miramar, Florida.
• Orlando, Florida.
• Lisle, Illinois.
• Exton, Pennsylvania.
• Bloomfield, New Jersey.