Why is my petrol car giving black smoke?

Why is your petrol engine car giving black smoke like an old diesel engine? The whole point of petrol is that it burns cleaner than diesel and is easier on the environment, so what’s the deal?

Is the petrol burning properly (Read about changing spark plugs here)? Did you accidentally put diesel in a gasoline engine car? Is your oil change overdue? In this post, we discuss why petrol engines give black smoke and how this problem can be fixed (for cheaper).

As car owners, our first instinct is to take the vehicle to a mechanic who tells us all kinds of scary things and gives us a massive estimate. If you take the wise step of researching a bit before going to the workshop, you may reduce your future invoice by half. So good job on coming here.

Why is my petrol car giving black smoke?

Is it normal for a petrol car to smoke?

When cars rack up tens of thousands of miles or kilometers, they eventually require some work. Sometimes its a simple oil change, or an engine tuning. Then comes the radiator coolant, the transmission oil change, the brake oil top up, and so on. After hundreds of thousands of kilometers, we start having bigger and more expensive maintenance tasks.

So in this case, the first thing you need to check is the age of your car.

Remember when your brand new or used car had invisible exhaust fumes except for some droplets of water? Well, its been a while. This black smoke problem in petrol engine cars appears in older cars that have hundreds of thousands of kilometers. This does not mean your car is dead or scrap metal. Its still running and getting you places isn’t it?

Can dirty fuel cause black smoke?

The black smoke coming out of your car is carbon laden emission. This is probably not coming directly out of your engine, but is a mixture of the cleaner emissions your engine and the carbon soot built up in your exhaust system over the years. Once you start getting black emissions in a gasoline engine car, you now know its time to check the exhaust system.

What causes black exhaust?

The most common cause of black smoke lies in the exhaust system, and not the engine itself (thank goodness). This is the part that starts at your engine, goes underneath your car all the way to the tail where you find the muffler and exhaust tip.

There are three parts of your exhaust system that could be causing the black smoke.

  1. The point attached to your engine (least likely)
  2. Catalytic converter (quite likely)
  3. The exhaust muffler or drum (also quite likely)

If the catalytic converter is not working anymore and spewing out the very stuff its supposed to clean, its simply a matter of replacing the catalytic converter under your car. If the catalytic converter still has some miles in it, then get your exhaust muffler cleaned.

How do I fix black smoke from my car?

Clean the exhaust pipe

At the end of your exhaust system is an exhaust tip where the emissions come out from. Just before that is a cylindrical drum we call the muffler. While its job is to dampen the sound of your car so that you don’t sound like need for speed, it tends to collect along of carbon soot on its walls. After several years, this soot begins to powder down and mix with your emissions. The result is black smoke.

If this is the case, you do not have to replace the entire exhaust system. Just get the muffler cleaned as per the below shown process.

Detach the Muffler from the exhaust

This step is self explanatory. If its a bolt on type muffler, un bolt it. If its a single seamless piece, some cutting and welding may be required.

Cut small incisions of both side of the exhaust drum

With a welder or torch, make small incisions on the front and back of the muffler drum. These small cuts will provide access to get inside the drum with a cloth, scraper, pry, or whatever tool you intend to use for the cleaning and scraping process. The opening on the other side (where you make the cut) will help the carbon build up exit the drum.

Apply some heat

Using a blow torch, heat up the inside walls of the muffler drum. This would help loosen up some of the carbon soot and make it easier to scrape or tap off.

Tap the drum with a hammer

With a small hammer, tap the exhaust drum at various points. This would also help that carbon build up fall off the inner walls.

Shake and Tap

After applying, heat, tapping it around, and scraping the inside, shaking the muffler drum is the best way for getting the black stuff out of there. Repeat this process until you cannot get anymore carbon out of there. The muffler should be way cleaner now than before.

Reseal the openings

Before attaching the muffler back to your exhaust system, close those small opening you made earlier, otherwise your car is going to sound weird. This is a job for a welder.

Re-Attach the muffler

Either bolt it or weld it back on.

Test your cars emissions for black smoke

Start your engine and push the gas. To properly test your exhaust system, push the gas all the way down repeatedly, letting the RPM go up and down multiple types. Vroom Vroom Vrooooooomm!! Vroom Vroom. Don’t just hold the pedal down at a constant rpm going vrooooooooo(10 seconds later)oooommmm. Hear the sound of a 2003 Honda Civic Engine.

If your petrol car is not putting out black smoke anymore, you’re good. If your emissions are black, you may have to change the whole system, including the catalytic converter.

Can I drive my car with black smoke?

Yes, after getting your exhaust system cleaned. Its a good idea to go out on a long drive on a highway where you can maintain a constant and high speed. This is will allow your exhaust to breather for a while and cough out any remaining carbon.

Fill up with Hi-Octane Gasoline

Hi-Octane petrol or higher grade gasoline is relatively cleaner than the lower grade regular stuff. Filling up with better quality fuel would further help cleanse your exhaust system and refresh your engine. Read: Does shifting your car to neutral at red lights save gas?

Your petrol engine car should be black smoke free for another few years.

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