Decoding the Smoke: What Your Exhaust Is Telling You

If you are driving along and notice exhaust from your own vehicle in your rearview mirror, take note. Any exhaust you can see is typically not a good sign. The color of the exhaust can give you a clue as to what is going wrong under the hood.

Black Smoke

If you are seeing black smoke from your vehicle, your engine has an imbalance of the air and fuel ratio in the combustion chamber. Partially burned fuel is entering the chamber when it shouldn’t. There are a few ways this could happen:

Poor driving.

When you put the engine in a higher gear than it needs, you are telling the engine to give it more fuel. Doing this injects more gas into the combustion chamber, which causes an imbalance in the air-to-fuel ratio. If this is the cause of the black exhaust, there is nothing currently wrong with your engine. If you don’t switch up your habits, however, you will cause damage.

Faulty injectors.

The fuel and air ratio might also be off if the injectors are damaged. If they are stuck open, they will inject too much fuel.

Poor fuel quality.

Bad fuel quality is the culprit for many different issues. Fill your engine regularly with quality fuel from trusted sources.

Air restriction.

Black smoke is usually due to an air restriction somewhere in the vehicle. Many places could be the source of the restriction:

  • Air inlet: A blockage could occur wherever air enters the engine. If an inlet piping collapses, the engine won’t bring in enough air.
  • Air filter: If you haven’t changed your air filter recently, it could be so dirty that it prevents enough air from entering the engine. Dirty filters are a common cause of black exhaust; luckily, they are also an easy fix.
  • DPF damage: If the diesel particulate filter (DPF) is damaged, it can restrict airflow.
  • Sensor failure: Engines have sensors that measure and adjust air intake. If the sensor is damaged, it may allow the wrong amount of air in.
  • Incorrect parts: Engines are complex machines with many different parts working together. If an incorrect part has been installed that does not fit your engine model, it could create an imbalance in the air-to-fuel ratio.

If you change the air filter in your vehicle (and you know you drive the vehicle in the correct gear), and the black smoke persists, have a trusted mechanic look at what might be happening.

White Smoke

If your exhaust is light or thin white, especially when the temperature is cooler, you typically have no cause for concern. This is actually water vapor that has somehow been trapped in the exhaust system.

A milky white smoke, however, merits closer inspection. Milky white smoke could come from a coolant leak in the head gasket or a cracked block or cylinder head. When the coolant reaches the combustion chamber, it blows out as milky white exhaust. Take your vehicle to be inspected soon because if your combustion chamber is full of coolant, then your engine probably does not have enough. Your engine will have a higher risk of overheating.

Blue Smoke

Oil burning in your engine creates blue smoke. It is never a good sign. When you see blue smoke, you will want to schedule an appointment for your vehicle ASAP.

Oil could enter the engine from different places. It could be entering different parts of the engine because it is the wrong type of oil (thinner oil will be able to go places, thicker oil won’t). Damaged or incorrect parts could allow oil to pass through them. Overfilled oil could cause the excess to burn. Something could be blocking the flow of the oil, which would cause it to burn.

None of the underlying reasons for the blue exhaust are quick fixes. You will need to do some sort of repair to your vehicle. Take your vehicle in soon, so you don’t find yourself stranded with a broken down car while looking up “24-hour tow service near me” on your phone.

Gray Smoke

If you see gray smoke coming from your vehicle, look closer at the exhaust. It can be easy to mistake blue smoke for gray. As mentioned above, blue smoke is not a good sign.

Gray exhaust can come from putting the incorrect grade of fuel in the engine. A clogged air filter could also cause gray smoke. If you smell a somewhat sweet burning odor, the problem could also mean your engine is burning transmission fluid and needs prompt, professional attention.

The smoke signals your vehicle sends you are its way of letting you know what is wrong. If you don’t catch the exhaust in time, keep Roadside Rescue in mind for any emergency towing services you may need.