Is dark engine oil dangerous or just normal?

Many drivers start to panic when the recently filled light engine oil quickly darkens or even turns black, because it is considered to be a sign of wear and tear, and it needs to be changed urgently. However, it is not always the case — in fact, darkening of the oil can indicate that it is doing its job effectively.

Jalopnik wrote about it.

Why does the oil turn dark?

Modern synthetic oils contain special additives, including detergents and dispersants. These additives begin to work immediately after the engine is started. They clean the internal surfaces of the engine from dirt, deposits, and sludge that inevitably form during operation. As the oil circulates through the engine, it collects these contaminants. That is why its color changes from light golden to dark brown or black.

In addition, the color of the oil darkens under the influence of high temperatures and oxidation. During the cyclic heating of the engine, when it warms up and then cools down, chemical additives also react to temperature changes.

Oil turns black especially quickly in diesel engines. This is because much more soot is formed during the combustion of diesel fuel than in gasoline engines. The oil effectively absorbs this soot.

Wear indicators

Darkening of engine oil is a normal process. The dark color indicates that the additives are working properly, cleaning and lubricating the engine. The color of the oil itself is not a reliable indicator that it needs to be changed.

It is much more important to adhere to the recommended oil change interval specified in the car's operating manual. The manufacturer takes into account all the features of the engine, the type of fuel, and the recommended brand of oil to determine the optimal mileage. That is why it is worth focusing on mileage or time, and not on the color of the fluid.

Ignoring the manufacturer's recommendations can lead to premature engine wear because, over time and mileage, additives lose their effectiveness, and the oil itself loses its lubricating properties, regardless of its color.

Read also:

Mixing up motor oils — Diesel vs. Gasoline explained

Can synthetic oil be used in an old car engine?