What Happens When You Don't Change Your Car Oil?
The conventional wisdom is to change your car's motor oil every 3,000 to 5,000 miles or at least once a year. Car manuals generally advise to switch the oil filter at the same time. If you don't, the engine wears faster and can even seize up, requiring replacement.
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The Function of Motor Oil
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Oil lubricates metal parts that slide past each other. This reduces wear and prevents friction that would make the engine too hot to function. If the parts were allowed to scrape, the pistons' precise machining would degrade over time, increasing the friction, rate of wear and operating temperature. If this self-reinforcing process eventually makes the engine too hot, the oil could all burn off. The engine would then get hotter still and the metal surfaces of the cylinders and pistons could melt, seizing the engine and making it unsalvageable.
Sludge
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As oil becomes dirtier, semi-solid dirty particulates precipitate out. This sludge can fill up and clog your oil filter to the point that oil no longer flows through it. Without filtration, the oil gets dirtier faster. This increases oil viscosity, eventually reducing the speed at which the engine turns. In other words, your RPMs can go down.
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Oil Pan
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The sludge can also accumulate at the bottom of your oil tank. When you finally change the oil, no oil may be able to flow out of the drain hole. You would then need to poke through the sludge with a screwdriver to open a path for the oil to drain out. You would also want to remove the oil pan to manually remove sludge buildup.
Oil Pressure
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Sludge could also clog up an oil passage, causing a drop in oil pressure. The oil would have trouble circulating, leading to a reduction in lubrication of the pistons and cylinders.
Degradation of Additives
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Oil manufacturers add carbon polymers to oil to increase viscosity at high temperatures and reduce it at low temperatures. These polymers degrade with use, losing their ability to adjust viscosity to the engine temperature. Again, this leads to engine wear.
Undetected Leak
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Without regular oil changes, your oil level could drop dangerously low without your being aware of it. You may have an oil leak or the oil could burn fast. Don't be surprised if your car burns half a quart per thousand miles. This rate isn't normal for cars in general but is normal for some car models.
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- Photo Credit Auto Engine image by Andrew Breeden from Fotolia.com
