How Dirty Engine Oil Affects Your Car

When your car is running, thousands of components within the engine move and generate immense heat and pressure. To ensure the whole system operates efficiently, there's a specially formulated oil that flows continuously through the engine as your car is moving. This oil is engineered to be effective within a specific service interval. When it becomes contaminated or degraded, the oil won't circulate as it should, and that can affect your car's health and performance. This is why it's essential for car owners to understand the functions of engine oil and how dirty oil affects their cars.

What Oil Does for Your Engine

Engine oil performs several critical functions. It lubricates all the moving parts within the engine as they operate at high speeds and under extreme pressure to keep your car running. This is essential to reduce friction, prevent metal-on-metal contact, and minimize wear on engine components. The oil also absorbs and disperses the heat produced during combustion and friction, and cleans the engine by suspending contaminants like soot, carbon deposits, and microscopic metal shavings, then carries them to the oil filter for removal. Without clean oil, these essential functions fail.

How and Why Engine Oil Deteriorates

Engine oil is engineered with a specific lifespan. Over time and mileage, engine oil is exposed to extreme heat, pressure, and contaminants, which degrade its chemical properties and reduce its effectiveness. Additives within the oil begin to break down, and the oil oxidizes. This process thickens the oil, diminishes its ability to flow properly through narrow passages, and reduces its capacity to form the protective film that prevents metal-on-metal contact between moving components.

How Dirty Engine Oil Affects Your Car

A dirty or contaminated engine oil doesn’t have the same ability to reduce friction, cool, or clean your engine as fresh oil does. When the oil isn’t changed regularly and becomes contaminated, friction between moving parts increases, heat builds up uncontrollably, and harmful debris like carbon deposits and metal particles accumulate within the engine. The result is accelerated wear, formation of sludge deposits that restrict oil flow, and increased friction, which raises operating temperatures.

Now, there’s a component designed to ensure the oil remains effective throughout its service interval—the oil filter. This filter removes impurities from the oil and prevents them from circulating through the engine. However, just like the engine oil, the filter itself has a limited lifespan. Over time, as it captures more and more contaminants, these particles begin to accumulate and eventually clog the filter. When the filter is clogged, oil can no longer pass through it efficiently, triggering the filter’s bypass valve. This safety mechanism allows oil to continue flowing to the engine, but it bypasses filtration, meaning unfiltered oil, filled with abrasive debris, circulates through the system.

Engine Oil Best Practices

Always adhere to the oil change intervals specified in your vehicle’s owner’s manual. These intervals are based on extensive testing by the manufacturer and take into account factors like oil degradation, contamination, and filter capacity. If you drive in harsh conditions—like extreme heat, towing heavy loads, or stop-and-go traffic—you might need to change it more often.
Always use the right type and grade of oil for your engine. Manufacturers design engines with specific oil formulations in mind, and using the wrong type can cause problems like poor lubrication or excessive deposits.
When changing your oil, always replace the oil filter at the same time. This ensures that contaminants from the old oil do not circulate through the fresh oil. Use high-quality oil filters that meet or exceed your manufacturer’s specifications. FRAM oil filters are designed to provide comprehensive protection for all types of engines and driving conditions throughout the entire OE-recommended oil change interval.
Regularly check the oil level and color. Dark, sludgy oil or a burnt smell are signs of contamination. Modern vehicles have oil quality sensors that indicate when a change is necessary.