How to Fix a Smoking Exhaust

What Causes a Smoky Exhaust?

Though your car’s engine burns gasoline or diesel all the time, burning such fuel doesn’t normally produce visible smoke. If you can see smoke, that means something is wrong: either your engine isn’t burning the fuel completely, or it’s burning something else that isn’t supposed to be there at all.

Identifying Smoke Problems

If your car is smoking, you can sometimes diagnose what’s causing the problem by looking at the type of smoke.

No, not like that.

Definitely not that.

We’re specifically talking about smoke coming out of your car’s tailpipe. If there’s smoke in the exhaust, that means there’s something burning inside the engine itself. The color of the smoke changes depending on what’s being burned.

• Black smoke: Thick black smoke is caused by your engine burning gasoline or diesel—the stuff it’s supposed to burn—but it’s not burning it up completely. That’s bad news, because it means you’re wasting fuel. You’re literally seeing your gas money go up in smoke. It increases your carbon footprint, and causes carbon deposits inside your engine/exhaust system. Black smoke comes from having the wrong fuel/air mix, which can be the result of a clogged air filter, a clogged injector, a dirty carburetor, a bad sensor, or even a computer glitch.

• White smoke: White “smoke” is actually water vapor, or steam. You’re not supposed to have water in your engine, so, again, this is bad. Really bad. Before you freak out, though, it’s important to note that having a little bit of white vapor when you first start your car is not unusual. It’s likely just the result of normal condensation within the tailpipe. As long as it’s minor and stops after a few minutes, it’s not a problem. But if you have thick white smoke that doesn’t stop after the car warms up, that is a problem. It could mean that you have coolant leaking into the cylinders, which happens when you have a blown head gasket, damaged cylinder heads, or a cracked engine block. None of these are cheap to fix. (Now you can freak out.)

• Blue or gray smoke: This is caused by the engine burning oil. That’s not good, but it’s also not uncommon. Older cars, especially, can start burning oil as the engine becomes worn. However, since being low on oil is a causes engine wear, this turns into a vicious cycle. Burning oil causes more wear, which leads to more oil burning, and before long you’re having to pay for a new engine—or a new car.

Sometimes it can be hard to tell exactly what color the smoke is. There’s a fine line, for example, between light gray and a dirty white, or a dark gray and black. The good news (sort of; we’re looking at the bright side here) is that if it’s burning enough oil or coolant to make smoke, there will be a noticeable dip in the oil or coolant levels. That means you can check your fluid levels to see which one is burning. (If neither is low, then we’re probably looking at black smoke, which will cause your car to have low fuel economy.)

How to Stop Your Car From Smoking

So how do you fix the problem? It depends on which problem you have.

• To fix black smoke: There’s an easy way, and a hard way. The easy, inexpensive place to start would be to simply add some complete fuel system cleaner to your gas tank. As you drive, it will automatically clean injectors, carburetors, and intake valves. Sometimes, that’s all you need to get your engine running cleanly again. (A smoky engine needs cleaning, anyway, so fuel system cleaner is a good idea regardless.) If that doesn’t work, you’ll need to take the car to a mechanic. That’s the hard way, or at least the more expensive one.

• To fix white smoke: Unfortunately, there’s no easy way here. And no, you can’t just ignore it and keep driving; it will eventually cause your car to overheat and could potentially ruin the engine. You’ll need to take it to a repair shop.

• To fix blue or gray smoke: The easy way is to add a bottle of Motor Honey Oil Treatment to your motor oil with each oil change. It’s specially designed to reduce oil burning and stop smoky exhausts. The hard way is an engine overhaul, which is about a hundred times more expensive and a thousand times more work. Needless to say, we like the easy way better.