How Does Engine Oil Get Dirty? Reasons And Symptoms

Engine oil is the lifeblood of any engine to work correctly. But you may be thinking, is this statement true? After knowing about the oil’s effectiveness, you can understand its truth. The functions of oil are to lubricate vehicle engine components, reduce friction and reduce component wear.

As a result, the engine gets dirty and changes color while performing its work. However, you don’t need to worry about how engine oil gets messy because it’s just doing its functions. Read on to learn the causes of dirty engine oil.

How Does Engine Oil Work?

Your vehicle’s engine lubrication system is made up of several components that work together to ensure smooth operation. One component of the lubrication system is the sump or oil pan. You can get this oil pan under the engine.

Another component of the lubrication oil system is the oil pump. It pumps and circulates motor oil through the vehicle engine. You can compare the operation of an oil pump to the heart in the human body.

The oil pump circulates oil through the engine, and this oil sucks the heat generated by the moving elements. Then, the heat is transferred to the sump, which is dissipated by air flowing over the sump. Additionally, this process continues while your vehicle is running.

A thin lubricating film is left on moving elements when engine oil is pumped under pressure through the engine. Also, the film helps create a slippery surface that separates the moving metal parts. In this way, it reduces friction.

What Is Dirty Engine Oil?

Dirty engine oil contains many contaminants and can no longer perform the work. Impurities in oil change its color and make it thicker. Oil travels through the engine. But dirty oil can’t lubricate the engine and transfer heat.

Dirty Engine Oil Symptoms

How And Why Does Engine Oil Get Dirty?

If your engine oil turns black and dirty quickly, there could be some reasons behind it. Now let’s see the reasons and symptoms behind engine oil getting dirty.

Dirty Engine Oil Symptoms

An oil change is a standard car service that car owners need to do regularly. Regular oil changes will increase the overall engine performance and extend your life. Now the question is, how do you know that your engine oil is dirty? Symptoms of dirty engine oil are as follows:

Knocking and Loud Noise

Engine oil prevents metal-on-metal contact by giving a lubricating film that helps make a slippery surface. Engine oil cannot perform this function if it is dirty. Therefore, the engine oil will make loud noises like hissing, knocking, and roaring. Make sure you change the oil before seeing this sign, which leads to severe damage.

Dark Oil

Clean engine oil contains an amber appearance but changes color when it gets dirty. Dirt and other impurities make the oil thicken. To know the oil level and color, check the dipstick. If the oil is dark and thick, change it as soon as possible.

Check Engine Light

The check engine light dashboard indicates a problem with your engine. When you see the oil change light, you should quickly pull over and check your engine oil level and color. Please don’t ignore this warning sign because it can lead to engine damage and costly repairs.

Oil Smell

The smell of oil inside your car means that there is a leak. The smell of oil mixed with the smell of exhaust fumes or gas means your engine is overheating. Please fix the overheating engine problem quickly before you damage your vehicle or start a fire.

Exhaust Smoke

Another symptom of dirty engine oils is exhaust fumes. When you see smoke while driving your car, it signifies dirty oil, an oil leak, or an engine malfunction. Hence, you need to go to an automobile workshop for a diagnostic test to know the problem.

What Causes Engine Oil To Get Dirty Fast?

Engine oil is not just oil but a mixture of friction lubricators, viscosity-supporting agents, and corrosion inhibitors, all of which play an essential role in keeping the engine moving smoothly.

Overheating Engine

Heat is one of the leading causes of engine oil breakdown. An engine under normal conditions reaches from 200 to 230 degrees anywhere.

However, overheating engine can rise much higher. Heat directly attacks the engine oil viscosity by disrupting airflow in the engine compartment and breaking down larger molecules.

Enhanced Oxidation

A natural process of an engine is oxidation. And it enhances over time and causes engine oil chemical breakdown. It is the heat in the presence of oxygen and the interaction between the engine oil molecules. Eventually, it reduces the lubricating effect of the liquid. Generally, the process rate is, however, higher under certain conditions.

Coolant Leak

Another pollutant that does not directly pollute engine oil but affects its molecular structure is antifreeze. Besides, it destroys the lubricating oil properties by increasing its viscosity which resists its soft movement with the engine elements.

With coolant in the system, you can expect a lot of problems with your engine as the lubricant becomes completely ineffective. After a coolant leak, your coolant system will face many problems if the lubricant becomes completely ineffective.

Your Engine Oil is Just Doing Its Job!

Yes, you heard it right! If the engine is working correctly, it is customary to be black and dirty. Think about how many times your engine oil has moved through your car’s engine! It is standard for engine oil to change color and viscosity after a certain period. You need to accept the fact and change the oil if necessary.

The Oil Filter Is Out Of Date

The primary duty of your car’s oil filter is to catch the pollutants present in the engine oil. However, it may not work as efficiently when it is old. As a result, your engine oil becomes dirty. So if you have an old oil filter, change it soon.

You’ve Waited Too Long For An Oil Change

If you wait too long to change your oil, it’s clear to get dirty. This is why you should consider regular oil changes.

Clean Vs. Dirty Engine Oil

Clean engine oil contains an amber color appearance. It lubricates the moving parts and increases the performance of the engine. Also, it doesn’t use much gas. Besides, with less effort, it helps your engine run more efficiently. On the contrary, dirty engine oil contains a dark or black color.

Dirt, pollutants, and impurities in the engine change its color. Harmful pollutants affect the oil’s viscosity and prevent it from performing its work efficiently.

Read More about Clean Vs Dirty Engine Oil

(FAQ)Frequently Ask Questions:

Q. Why is my oil dirty after an oil change?

Because it’s not possible to drain all the old oil from the engine. A ‘dry fill’ can be 4.6L and a drain 4.4L. That means 0.2L of oil in the engine never comes out. That oil is dirty, and the new oil is enough to turn black.

Q. Does synthetic oil get dirty?

Yes, conventional and synthetic oil gets dirty. But the difference between these two is that synthetic oils have a longer useful life and work better than traditional oils.

Q. What Causes Engine Oil to Black?

The primary reason engine oil turns black is because it performs its job. Just read the Causes of Dirty Engine Oil section in this article for a more detailed answer about this topic.

Final Word

To conclude, we hope we were able to answer your questions; How does engine oil get dirty? You shouldn’t panic when your engine oil gets messy, but you should be concerned if it gets dirty too quickly. To avoid excessive damage, make sure you change the oil regularly when noticing signs of dirty engine oil. We hope you had a good read.


I am Engr. Z Eusuf Lubricant Specialist, Mechanical Engineer & has been working with engine lubricants for a long time and knows what makes them work best. I can help you find the right oil for your needs, and I have tips on how to keep your engine running at its best.

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