The color of your car exhaust, believe it or not, can tell you much about the condition of your vehicle. It’s one of the reasons I always recommend that used car buyers not only start a car, truck, or SUV, but pay close attention to the nature of the exhaust that appears from the tailpipe. But you should also check the exhaust on your existing vehicles, too, as part of a regular system of spotting problems and getting them fixed.
Lest you think checking the exhaust color sounds a little like reading tea leaves or divining the bumps on someone’s head, it’s really not quite that esoteric. Your car exhaust is the end product of how well the engine performs and what you put into the engine to fuel and lubricate it. By nature, junk in usually means junk out so always watch what you add to your car, truck, or SUV.
Despite using quality fuel and only the recommended oil, what comes from the car exhaust is a mess, you have reason to worry. Something within the core components of your vehicle is causing fuel and/or oil to break down, or fail to combust, in a way that indicates you have a problem. The root of the problem probably lies well ahead of your exhaust system itself, usually within the engine.
In a well maintained vehicle that operates in peak condition, you really should not be able to see the exhaust much at all. On a very cold morning, you may spot more apparent smoke, but this is simply the difference in temperature between the exhaust coming from a warm or warming engine and the temperature of the air. This is similar to what you see when you breathe or speak outdoors on a cold day: when you breathe, you see the condensation in a puff of mist coming from your mouth.
When you have cause for concern is when you can see the exhaust regardless of how warm the day may be. Different colors or qualities to the car exhaust usually indicate different degrees of trouble. A pale gray color isn’t bad and some consider this a normal color.
But the darker the exhaust gets, the worse a symptom it portends. For example, black or dark blue oily smoke alerts you to a problem with the engine. It may not even be a deep worry, because you or someone who services your vehicle may be adding too much oil. The overage on oil has to go somewhere, so the car sends it back through your exhaust.
Yet oily smoke can also signal a failure in the integrity of your engine: oil is not staying where it should be so it’s coming out through the exhaust. You sometimes see this on very old, poorly maintained vehicles, especially ones with lightweight aluminum engines that degrade after years of hard use. The moment you begin to see such exhaust appear, you need to schedule a trip to a trusted garage or mechanic for a full engine inspection. You may need a serious repair such as a ring job. In a worst case scenario, you may need to replace the engine.