Why Does Your Engine Oil Turn Black & What Does It Mean?

When you put new engine oil in your car, it has a beautiful golden hue. Over time, its consistency, quality, and color start to darken. But why does engine oil eventually turn black?

Engine oil turns black due to heat cycles, soot, carbon, dirt, or other contaminants in the oil. However, this dark color doesn’t necessarily mean that it’s time to change the oil. It’s just a natural byproduct of soot particles and heat that are too small to damage your car engine. 

As a general rule, the engine oil color doesn’t dictate its efficiency. As long as you check the oil regularly and change it according to the vehicle manufacturer’s instructions, you’re not going to face any problems. Let’s take a closer look at what causes your engine oil to turn black.

Why Does Car Engine Oil Turn Black?

Engine oil becomes black simply because it becomes dirty over time. Black engine oil is not something that you should be worried about.

However, if your dipstick comes out gold, then it’s a cause for concern because it means that your engine oil isn’t suspending nasty particles like carbon and other contaminants.   

Several things can turn your engine black including carbon buildup, dirty air, and other residues. Even in areas with low air pollution levels, engine oil isn’t able to maintain its golden hue for long.  

Let’s now delve deeper into the factors that can cause your engine oil to turn black:

Heat Cycles

Heat naturally darkens engine oil. 

When you drive to work or school every morning, your engine ranges between the operating temperature of 90 and 104 C (194 to 219 F), heating the motor oil. The oil then cools down while your car is in the parking lot.   

The engine oil is exposed to heat again on your way home and is repeated again and again, day after day. 

Some additives found in engine oil easily darken when heated compared to others and also normal oxidation can darken oil. 

Oxidation happens when oxygen interacts with engine oil and causes chemical breakdown similar to how oxygen turns iron to rust and a cut apple to brown. The oxidation process accelerates due to high heat. 

Engine Deposits 

While driving, the engine oil not only comes into contact with all the engine parts but also with the deposits that may be found on them. Typically these carbon deposits are black in color and they can cause the engine oil to turn black quickly. 

Soot

While heat causes oil to darken, soot turns the oil black. Most people typically associate soot with diesel engines, but soot is also produced by gasoline engines, especially modern gasoline-direct injection engines.  

Incomplete combustion results in soot. Since soot particles are smaller than one micron, they usually don’t cause any engine wear. If these particles accumulate and become larger wear-causing contaminants, they’ll be filtered out.  

It’s commonly assumed that black engine oil means that it has become too saturated with contaminants or worn out to protect your engine and needs changing. Not necessarily. 

Discoloration of oil is typically caused by soot particles and heat and is not an indication of the state of the oil itself. Dispersants and detergents present in the engine oil are what cause it to become black, while it’s carrying on its job of cleaning the engine and moving particles to the oil filter. 

Why Does My Engine Oil Turn Black So Fast?

Engine oil protects the engine against wear and tear by preventing it from coming into contact with objects like carbon and rocks. However, with usage, the engine oil starts to break down and eventually turns black due to the presence of carbon and residual oil. 

Another reason that causes your engine oil to get dirty quickly is high temperature. Engine heat causes oil to break down into carcinogenic compounds and form sludge which can be quite hard to remove. It can also cause severe engine damage.  

One reason why engine oil turns black is that it contains a pigment that, when exposed to air, forms soot. As a result, your engine’s performance is affected and there’s a greater chance of engine damage.

Changing the engine oil regularly is crucial as it helps to remove carbon and residual oil buildup and keeps the engine running smoothly.

Is It OK for Engine Oil to Be Black?

Yes, it’s okay for engine oil to be black as color doesn’t necessarily mean anything. Oil color can be very dark and it can still perform effectively.

Even though new oil is golden in color, engine oil eventually gets darker because of contaminants, high heat, and additives that work as detergents for cleanup.  

If you want to protect your engine from damage, then it’s essential to perform regular oil and filter changes. This should be done every 7,500 miles or six months. You can also consult the manufacturer’s recommendation and change the oil accordingly. 

Remember that dirty oil can be more dangerous for your car engine than having no oil at all. If the oil becomes overwhelmed with metal, dirt, and other debris or loses its viscosity, it can become quite corrosive and effectively speed up the wear and tear of the various parts of your engine.  

Dirty oil also decreases fuel economy. As a result, the engine is very likely to overheat or just break down entirely.