Does Oil Color Affect Engine Performance?

After a period of use, motor oil will change to a darker color. This often makes many car owners concerned, prompting them to immediately replace it with the best automotive oil for their beloved vehicle. However, is this assumption truly accurate? Does the color of the oil affect the performance of the car? Let’s explore the answers with Huỳnh Châu in the following article.

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Does the Color of Oil Really Determine Vehicle Performance?

1. Additives Determine the Color of Motor Oil

Before discussing why oil turns black after a period of use, let's first understand the “original” color of motor oil.

The color of motor oil is primarily determined by the additives it contains. Some oils are light brown, while others are darker, depending on their chemical composition. For example, AMSOIL Signature synthetic oil is light red, while Repsol oil has an amber and quite transparent color.

Additionally, some brands add coloring agents to the oil for marketing purposes. For instance, MolyGen oil is dyed fluorescent green to leave a stronger impression on customers. Therefore, it is not possible to rely solely on color to determine the best automotive oil.

The color of motor oil is influenced by additives.

2. Why Does Engine Oil Gradually Turn Black?

Now, let’s take a closer look at why engine oil changes to dark brown or black. According to technicians, there are three main reasons:

The first is contaminants. During circulation, the dispersants in the oil clean the engine and keep dirt and carbon deposits suspended (small particles floating in the fluid).

Thus, even if you use high-quality automotive oil, color change will still occur. This is a normal indication that the oil is effectively cleaning itself.

Carbon deposits are one reason the oil turns black.

Furthermore, the engine's thermal cycle causes the oil to darken. Specifically, while the vehicle is running, the engine reaches temperatures of about 195 °F – 220 °F (equivalent to 90 °C – 104 °C), causing the oil to heat up. Once the vehicle stops, the oil cools down. This continuous process leads to oxidation, which changes the oil's color.

Another reason for color change is soot. Even when using the best motor oil filters, soot cannot be completely removed from the oil.

Typically, oil filters can only block soot particles larger than 5