What Causes White, Blue, Black, or Gray Exhaust Smoke?

What Causes White, Blue, Black, or Gray Exhaust Smoke?

Last Updated May 7, 2024 | Meghan Drummond

No one wants to see smoke coming from their exhaust, but the color of the smoke coming out of the tailpipe can give you important insights about what might be wrong with your car. Checking the color of exhaust smoke can also help you determine whether or not to purchase an older classic car by helping you to gauge how much work you might be signing on for.

As a general rule, black smoke from your exhaust means your car is burning too much fuel. Blue smoke means your car is burning oil, and billowing white smoke from your exhaust can mean you're burning engine coolant. Gray smoke from your exhaust can have several causes, but it can indicate you are burning transmission fluid. Check out the guide below for a full explanation of each of these exhaust smoke color meanings.

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What Causes Blue Smoke From the Exhaust?

Blue smoke usually appears in the morning when your engine starts up for the first time of the day. Blue exhaust smoke indicates that your engine is burning oil. Though this is primarily a problem in older cars, not taking care of maintenance issues can cause oil burning regardless of year.

It’s possible that your blue exhaust smoke is caused by simply having too much or too little oil. If there’s too much oil it gets into the combustion chamber, one of the many places in your car where you absolutely don't want oil.

If there’s too little oil, it can become overheated and overly viscous which also allows it to get into your combustion chamber.

To find out if this is the cause of your blue smoke, you should first check your dipstick. If it’s above the "full" line, you’ll need to drain and dispose of the excess. If it’s under the "add" mark you’ll need to add oil.

If you’ve fixed your oil level and are still seeing blue-colored exhaust smoke, then there are a few other reasons your car could be burning oil. The root cause of the oil burning can be anything from a leaky head gasket to a broken piston ring. If you’re driving a diesel vehicle, it’s possible that you have a faulty glow plug. All of these are issues that are best fixed quickly. If you don’t fix the issue it can become a compounding problem. A car burning oil risks fouling its spark plugs, overheating its catalytic converter, or even blowing its motor. Your best bet is to get your vehicle to a mechanic quickly before what could be an inexpensive PCV valve repair becomes a motor that needs to be replaced.

blue exhaust smoke coming from tailpipe

What Causes Black Smoke From the Exhaust?

Black smoke means that your engine is burning too much fuel. This particular problem does seem to affect diesel engines at a higher rate, but the steps to fix it are largely the same. Sometimes if you’re carrying a heavy load with a diesel truck you’ll see a small puff of black smoke, but even that should be minimal in modern well-cared-for engines. Whether you are running a gas or a diesel engine, you shouldn’t see black plumes of smoke issuing from your tailpipe, and it’s a clear sign that the engine isn’t being cared for properly. Obviously, you want your car to use as little fuel as possible, so burning extra is a problem that needs a quick solution.

The first thing to check is the air filter. If your engine isn’t getting enough air, then more fuel will be burnt. Checking and replacing the filter is easy. If your air filters are clean, then you have a few options. You can try a fuel additive to clean out any buildup that exists in the fuel injectors or cylinder chambers, or you can take it to a mechanic to see if your engine rings need to be replaced.

Though many people panic when they see black smoke thinking "fire" it’s actually one of the easiest problems to diagnose and fix. You’ll want to address it quickly though since your car is literally burning your hard-earned money until it’s fixed.

Black exhaust coming from tailpipe

What Causes Gray Smoke From the Exhaust?

Gray exhaust smoke is a bit of a mystery. Is it very light black smoke? Bluish-tinted white smoke? Unfortunately, because ‘gray’ is such a wide color band, it can be a minor variant of any of the other colors or its own thing entirely. Truly gray smoke is most frequently caused by burning transmission fluid.

Checking your transmission fluid is easy, and by evaluating the fluid on the dipstick you can learn a lot. If the fluid is dark or smells burnt, you may just need to change your transmission fluid. If the fluid looks fine or changing it doesn’t fix the issue you’ll want to get your car to a mechanic quickly. A transmission failing while driving can be very scary and even lead to an accident.

Gray smoke coming from tailpipe

What Causes White Smoke From the Exhaust?

Thin white smoke (especially on a chilly morning) is nothing to be concerned about. Thick white smoke, on the other hand, can indicate a problem. In particular, it could mean that your engine is burning coolant, which could mean a problem with a head gasket or a cracked engine block. These are big repairs, but it’s important to address needed repairs sooner rather than later. If the coolant leak mixes with the oil in your car it’ll create a much more difficult problem to correct.

Thick white smoke coming from tailpipe

Any color smoke coming from your car’s tailpipe is a sure sign that something needs to be addressed. Like with most repairs, you’ll save yourself money down the line if you’re able to take care of it before your dashboard lights up to tell you it’s time to "service engine."

It’s important to remember that most of what’s coming out of your exhaust system is toxic and carbon monoxide fumes can be fatal. Upwards of 370 people die every year from carbon monoxide poisoning, and you don’t want to add to that number. Be safe, and if you have any doubts about performing repairs yourself, take your vehicle to a trusted mechanic.

This article was researched, written, edited, and reviewed following the steps outlined in our editorial process. Learn more about CJ's editorial standards and guidelines.