Car owners usually get alarmed when they discover that their engine oil has quickly darkened. It doesn’t matter whether you have a completely new car or a used one, even restored from wrecked cars. This situation can occur to any driver. That’s why we decided to figure out the reason for darkening engine oil. It is also important to reveal what to do in such cases, if it is a significant issue, and how to use the car.
Why Does Engine Oil Darken?
First, it is necessary to realize that the concepts of blackened and darkened oil are two different things. In engines with low mileage, the lubricant will keep its original amber or honey-brown color after pouring. In all other cases, the “fresh” oil will inevitably darken after a while. Why does this technical fluid change its color?
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Cleaning Motor
Many car owners believe that the causes of darkened oil can be engine problems or poor oil quality. Without any doubt, we note that these statements are mistaken, and here is the explanation why. In addition to lubricating rubbing parts, engine oil also performs the function of cleaning the engine. Special detergent additives that make up high-quality engine oil dissolve products of incomplete combustion of fuel. The lubricant circulation in the motor occurs in a closed loop—the oil is removed from the crankcase by an oil pump, and under pressure it’s supplied through the oil channels to all nodes, after which it again flows into the crankcase, taking with it all kinds of impurities, fuel combustion products, and corrosive elements. Soot particles in oil give it a dark color, although the lubricant’s operational properties are not affected—it continues to fully perform its functions. That’s why the oil can be safely used until the time of the planned oil change comes.
Remnants of Old Oil
There is another reason for the lubricant color change. The old oil remains in the engine after replacement. Regardless of the car mechanic’s qualification, it’s impossible to completely get rid of the old lubricant when it is changed and, in any case, at least about 1 liter of old, darkened oil stays inside the engine. Fresh grease, mixed with the remnants of the old one, will inevitably get a darker color.
Poor Quality of the Lubricant
Mechanics and experienced drivers often highlight the engine oil’s low quality as one more reason for its darkening. Some manufacturers, trying to reduce the cost of producing lubricants, save on special additives to them. Such oil oxidizes and darkens in contact with air. The engine grease will also change its color in case of severe engine contamination, use of poor-quality fuel, or forgetfulness of the motorist who did not change the oil filter during the lubricant change.
Causes of Engine Oil Blackening
The situation is different when the oil does not darken but turns black. It is not difficult to determine this. If black stains remain after wiping the oil dipstick, this indicates that the lubricant simply burns in the engine. Most often, this happens when the piston group is already sufficiently worn out. Then you can still feel the smell of burning that is common with this breakdown.
Violations in the Engine Cycle
It’s also important to remember that excess gasoline may not detonate in the engine cylinders, getting into the oil and changing its composition, which makes the lubricant bad for further use. Along with that, there is a decrease in motor power, rising fuel consumption, and more intense engine wear. In this case, we recommend thinking about repairs.
Motor Overheating
One more reason for oil blackening can be the lubricant overheating in the engine. With an improperly selected viscosity parameter and frequent vehicle operating at high speeds, the oil works at the limit of its capabilities and begins to boil. At hot temperatures, the grease dissolves all harmful impurities. As a result, the color of the oil may become black, not dark. Further use of such oil is impractical because it not only doesn’t have cleaning properties but can also lead to malfunctions of the oil pump and other units.
Why Oil Color Stays the Same?
We must admit that it is even more dangerous if the oil continues to keep its original color after a long service life. The reason for this is not the absence of pollution in the engine but the poor quality of the lubricant, which simply does not cope with its cleaning function. If you decide to change the motor oil to a good one from a reputable manufacturer in this situation, it will quickly turn dark. It is because the new grease will deal with all the dirt that is still in the engine after a low-quality product.
Wrap Up
The main thing to remember is that the dark (not black) color of the motor oil is not yet a reason for alarm. If the oil pressure and its level in the lubrication system remain within the normal range, the engine doesn’t overheat, and the Check Engine warning doesn’t appear. In this case, continue to operate the car, keeping in mind the planned replacement of motor oil. The driving distance parameter varies from car to car and can range from 3,000 to 13,000 miles. At the same time, if you find a thick black mass or liquid oil emulsion on the dipstick instead of the normal lubricant, you’d better immediately go to the service center. It means that your vehicle’s motor needs urgent diagnosis and subsequent repair.