7 Reasons There Is Smoke Coming from Your Exhaust


Your car has an exhaust pipe for a reason. During the combustion process that powers the vehicle, a mixture of air and fuel is burned, then must be expelled. The used-up gaseous mixture is pumped out of the engine through a series of pipes and filters and is known as engine exhaust emissions.

During ordinary operation, the fuel-air mixture is odorless and colorless. There does not appear to be anything exiting the tailpipe when seen from behind a properly operating automobile. Smoke exhaust that is something other than odorless and colorless is a sign—a smoke signal, if you will—that the vehicle is not operating at peak efficiency. More than likely, there is a problem that requires attention.

Here are seven reasons you might be seeing smoke coming from your exhaust, and what to do about it.

1. You Are Experiencing Condensation

Let’s start with the best-case scenario. You start your car on a cold morning and wispy white smoke from the exhaust pipe puts a scare in you. If the emissions return to normal after a minute of the vehicle warming up, breathe a sigh of relief: You have just been introduced to the smoke vs. steam scenario.

On cold days, the gaseous fuel-air mixture being emitted from your exhaust pipe condenses into liquid while sitting in a cold vehicle. When the car starts up, heat is produced, turning the liquid into steam, which is the white smoke exhaust you are seeing in that case. Once the car warms up, the emissions return to their normal colorless gaseous state.

2. You Have an Oil Leak

White smoke exhaust not related to condensation is commonly the result of an oil leak somewhere in the system. Motor oil is a viscous fluid designed to lubricate moving parts like pistons and keep them running smoothly. When the oil leaks into the combustion chamber, it mixes with the fuel and air being ignited and gets blown out of the tailpipe along with them. The result is white or bluish-white smoke.

This is a problem because oil does not belong in the combustion chamber. It interferes with the process and corrodes spark plugs. Even worse, it reduces the amount of oil lubricating those moving parts. If the leak is fast enough or goes on for a long enough time, your car can run dangerously low on oil and cause the engine to seize up.

Oil can leak from a variety of locations under the hood, but the most common is at the joints when o-rings, gaskets and other seals fail to perform. Additives like  BlueDevil Stop Smoke & Engine Repair is specially formulated to rejuvenate worn seals and prevent oil loss when a hard part repair isn’t an option. Simply pour half of a bottle into the crankcase with the engine off and drive the car for about 100 miles. The white smoke should disappear. The rest of the bottle can be saved for the next oil and filter change.

Oil leaks on a car are almost always the result of bad seals, but they can come from a variety of other sources, like a damaged oil filter or blown head gasket. Diagnosing the source can be tricky and might require the help of a trained mechanic.

3. You Have a Blown Head Gasket

Let’s talk a little more about a blown head gasket because that is a big issue. The head gasket sits on top of the engine block, separating it from the cylinder head. It is the barrier between the combustion chamber, where fuel and air are ignited, and the cylinder, in which pistons pump up and down, powered by the little explosions in the engine. The combustion chamber should contain only fuel, air and spark, and the cylinder only requires lubricating oil to keep the pistons moving smoothly inside it. The area around the combustion chamber is bathed in coolant to keep the entire operation from overheating.

When the head gasket is damaged or cracked, it allows fuel and heat into the cylinder, and oil and coolant into the combustion chamber, a potentially catastrophic combination on both ends. One sign the problem is the head gasket, and not something else, is the presence of smoke from the exhaust when accelerating more than when it is idling.

Oil and/or coolant burned in the combustion chamber creates the white smoke, indicating the head gasket must be repaired or replaced. Unfortunately, this is an expensive job—usually north of $1000—because nearly the entire engine must be disassembled to reach it. But it is necessary because the head gasket’s job is so critical that failure isn’t an option.

4. You Have a Coolant Leak

White exhaust smoke from a coolant leak is the easiest kind to diagnose because the antifreeze in coolant has a sweet smell that comes out of the tailpipe when coolant is leaking. A great way to verify that diagnosis is to check the coolant level in the coolant reservoir and observe whether it is low.

Coolant tends to leak from one of four sources:

  • the seals connecting various parts of the cooling system
  • the hoses that transport the coolant
  • the reservoir itself
  • a blown head gasket

If any kind of seal, like an o-ring or gasket is the culprit, and an actual repair isn’t possible, it can be fixed with a bottle of BlueDevil Coolant Stop Leak. The specially designed formula is guaranteed to seal leaks throughout your vehicle’s cooling system, stop antifreeze loss, and keep your vehicle in safe operating condition.

To use BlueDevil Coolant Stop Leak, with the engine cold, remove the radiator cap and start the engine, turning the heater up full blast. Slowly pour a bottle into the radiator. Restore the cap and let the engine run for 45 minutes so the product can circulate throughout the cooling system. BlueDevil Coolant Stop Leak bonds with materials in the seals, repairing cracks and restoring their vitality.

If the problem is a hose or reservoir, you can attempt to find the leak and replace the offending hose or reservoir, or take the vehicle to a mechanic. A blown head gasket is better left to the car care professionals and really advanced DIYers because so much can go wrong when disassembling and reassembling large parts of the engine. Either way, it is important get the issue fixed. Coolant leaking into the combustion chamber is a double problem for the engine—it can overheat from coolant loss and run rough from coolant in the fuel.

5. Your Car’s Computer Is Not Working Properly

A faulty engine control unit is good news and bad news when your car is smoking. It is good news because it is most often easily and inexpensively fixed. It is bad news because you probably can’t repair it yourself.

When the engine control unit gets out of whack, it sends bad information to the fuel injectors, and they squirt fuel into the combustion chamber incorrectly—either the wrong amount or at the wrong time. The result is unburned fuel that causes exhaust smoke.

If the computer goes haywire, there is one tactic you can try to reset it—disconnect and reconnect the battery. It’s a bit like turning off your laptop when it has a glitch: Sometimes it just works. If that doesn’t resolve the problem, a trip to a mechanic is in order for a diagnostic test and reprogramming. Few DIYers have the expensive diagnostic equipment necessary hanging around in their garages.

6. Your Car’s Fuel Injectors Are Bad

Fuel injectors can go bad even if the computer is working well. A bad fuel injector can be replaced relatively easily by disconnecting the battery and removing the fuel rail, which houses the injectors, from the intake manifold. Before installing new injectors, dip their tips in engine oil for a better seal.

7. You Have a Cracked Engine Block

Along with a blown head gasket, this is the nightmare scenario. A cast-iron engine block is designed to withstand the extreme heat and cold, rattling, shaking and pounding that every engine endures, but sometimes the excessive heat or cold is just too much for it.

Engine blocks can crack in different ways and places, but often they involve coolant leaking into the combustion chamber and producing white smoke. A cracked engine block should be last on the diagnostic list, but if every other possibility is eliminated, it should be examined.

If it isn’t financially feasible to replace the engine, BlueDevil Radiator and Block Sealer bonds with the cast iron, as well as other metals, and seals blocks permanently to keep your car on the road. With the engine cold, remove the radiator cap and start the engine, turning the heater up full blast. Slowly pour a bottle into the radiator. Restore the cap and let the engine run for 45 minutes so the product can circulate throughout the cooling system.  Top the system off with clean water or antifreeze once the engine cools back down.

There are other, less common, reasons smoke is coming from your exhaust, all of which are threats to the proper functioning of the vehicle. Whatever the cause, getting it fixed sooner rather than later will ensure your car or truck continues to run properly.

BlueDevil Products can be found at AutoZone, Advance Auto Parts, O’Reilly Auto Parts, NAPA, Parts Authority, Auto Value, Bumper to Bumper and other major auto parts retailers.

2 responses to "7 Reasons There Is Smoke Coming from Your Exhaust"


  1. Charles on April 21, 2022 at 7:22 am

    My ml350 emits white smoke from the tailpipes when you start the car and continues to smoke even after warming up, but when I drive the car for some time, say 20 minutes, the white smoke stops coming out. What could be the cause?

    • BlueDevil Pro on April 21, 2022 at 8:33 am


      Thank you for asking about your Mercedes Benz. White smoke billowing from the exhaust pipe would be one of the tell-tale signs of a blown head gasket. Is the vehicle overheating at all? Have you noticed a loss of water/coolant? Please contact our technical support line at 888-863-0426 so that we can get a little better understanding of the vehicle’s condition and be able to make any appropriate recommendations.

      Thank you!


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