Yes, a car's oil absolutely gets old. It's not just about the miles you drive; time itself degrades oil. Even if your car sits in the garage, the oil inside the engine deteriorates due to exposure to oxygen, moisture, and temperature fluctuations. This process, called oxidation, turns the oil acidic and sludgy, losing its protective properties. For most drivers, hitting the mileage interval first is common, but if you drive less than 5,000 miles a year, you should change your oil based on the time recommendation in your owner's manual, typically every 6 to 12 months.
The aging process involves several key changes. Additive depletion is a major factor. Engine oil contains a package of chemical additives that perform specific jobs: detergents to clean, dispersants to hold contaminants, and anti-wear agents to protect metal surfaces. These additives get used up over time. Moisture contamination is another issue, especially from short trips where the engine doesn't fully heat up. This water mixes with the oil, forming acids that can corrode engine internals.
You might notice signs of old oil. It often darkens from a golden amber to a thick, black consistency. In severe cases, a low oil pressure warning light might flicker because aged, thin oil can't maintain proper pressure. Following the manufacturer's schedule is the best defense. The following table outlines typical oil change recommendations based on oil type and driving conditions.
| Oil Type | Severe Service Interval (months/miles) | Normal Service Interval (months/miles) | Key Considerations |
|---|
| Conventional | 6 months / 3,000-5,000 miles | 12 months / 7,500 miles | Best for older car models with simple engine designs. |
| Synthetic Blend | 6 months / 5,000-7,500 miles | 12 months / 7,500-10,000 miles | A good balance of performance and price for SUVs/trucks. |
| Full Synthetic | 12 months / 7,500-10,000 miles | 12 months / 10,000-15,000 miles | Offers the best protection against thermal breakdown and oxidation. |
| Extended Performance Synthetic | 12 months / 10,000-15,000 miles | 12 months / 15,000-20,000 miles | Formulated for longer intervals and extreme conditions. |
