Motor oil lubricates the engine and absorbs heat, enabling the engine’s internal parts to work efficiently without overheating. As oil ages, it begins to lose its protective properties and must be changed. When engine oil turns black, however, that doesn’t always mean a change is imminent. Here’s how to tell when it’s time for an oil change.
Amber That Won’t Withstand the Ages
A heat cycle represents each time your engine reaches its normal operating temperature, typically somewhere just below 220 degrees Fahrenheit, then cools down again. Each trip to the store, commute to work and trek home from your children’s activities means your engine will heat up, then cool down. The more trips you take, the more heat cycles your engine completes.
Besides the heat cycle, contaminants will also darken engine oil. Tiny metal particles from engine parts will break free and circulate in the oil. The dust and dirt kicked up from the road and not trapped by the oil filter is another contributor to the oil’s darkening process.
Additives Cause Blackness
Engine oil also includes additives — chemical compounds designed to improve lubricant performance. Modern engines require these additives, found in both petroleum-based and synthetic oils. Without additives, your engine will fail. With them, your oil will darken, regardless of the number of heat cycles and abrasives present.
The best way to determine when the motor oil needs a change has everything to do with the maintenance intervals as outlined in your owner’s manual. If your engine takes synthetic oil and can go 10,000 miles between oil changes under normal driving conditions, then your oil is likely fine. However, if your driving habits fall under the severe-duty schedule — including frequent short trips, dusty roads and extreme temperatures — then you’ll need to change your oil more often. Again, consult your owner’s manual for the correct change intervals.
Just as motor oil will gradually transition from amber to black, there are other signs that an oil change is necessary. Some of these signs may quite possibly point to a related problem.
For instance, if the engine oil contains more than the usual trace amount of water, it will appear milky and diluted when you pull the dipstick. Water droplets clinging to the end of the dipstick are especially problematic.
This is a serious problem, one possibly caused by driving through flood waters. If this is the case, don’t start the vehicle. At a minimum, you’ll need to remove the oil and oil filter and flush out the oil pan. Next, add new oil and an oil filter, then drive your car for a few hundred miles before changing both again. However, for a long-submerged vehicle, you’re looking at a complete engine teardown.
Another problem to consider is oil that has a foamy or milky appearance along with a cream-like color. This is a clear sign of a head gasket leak, also confirmed by white smoke emanating from the exhaust or an increased consumption of coolant. Have the required repairs performed, then treat your engine with new oil and a new filter.
When your engine oil turns black, it may or may not be time for an oil change. It is a good idea to keep an eye on the color of your engine oil, though, as it can indicate other issues. When in doubt, consult your owner’s manual or a trusted mechanic.
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Matt Keegan has maintained his love for cars ever since his father taught him kicking tires can be one way to uncover a problem with a vehicle’s suspension system. He since moved on to learn a few things about coefficient of drag, G-forces, toe-heel shifting, and how to work the crazy infotainment system in some random weekly driver. Matt is a member of the Washington Automotive Press Association and is a contributor to various print and online media sources.