Why the oil is black after changing

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Many drivers wonder why oil remains black after changing, and no matter whether it is a diesel or gasoline engine. But we will tell you everything in order.

Engine oil turns black when soot and other combustion products enter the cylinders. An average of 90% of the volume is drained when it is replaced, while the remaining 10% remains in the crankcase, cylinder head, oil channels, and so on. You can’t completely remove it from the engine. Accordingly, when filling a new one, it mixes with the old black and, of course, darkens a little.


When changing the oil, many use flushing, warm up the engine and let it work on the flushing from 5 to 10 minutes. But again, when it is drained, 10% of the oil and some flushing still remain in the engine. So it’s up to you to decide whether or not to flush the engine.


Which engine oil is suitable for your car depends primarily on whether you have a gasoline or diesel engine. Diesel and gasoline engines require different engine oils.

For this reason, car manufacturers determine engine oil requirements, as well as replacement intervals specifically designed for each model.

In the operating instructions for your car you will find the required engine oil classification and specifications.

The SAE viscosity grade, API classification and ACEA specification are important. Some car manufacturers set their own test standards. The engine oil label indicates whether it meets the vehicle manufacturer’s required standard (e.g. VW 503.00).

If you don’t have an operating manual or service book to check which engine oil your car needs, you can search the Internet for the necessary information. For example, consultant Motul oil, Castrol.

In addition to the appropriate manufacturer’s engine oil that is right for your car, you will also see what viscosity grade it should have.

The choice between mineral and synthetic oil is a matter of personal preference. Synthetic are usually more expensive special oils that should help save fuel and provide more cooling.

Engine oils for summer and winter use.

In the area of motor oils, a distinction is made between seasonal (used either in summer or winter) and year-round use.

The corresponding SAE viscosity grade is indicated in the note in the engine compartment.


  • The lower the first number (5), the lower the lower temperature limit (viscosity at low temperature) at which the oil still has sufficient fluidity. 5 means that it can be used up to an external temperature of -30° C.
  • The higher the second number (30), the higher the high-temperature viscosity. 30 means that the engine oil can be used up to an external temperature of 30° C.
  • W means “winter”. In the case of seasonal oil, the classification is as follows:
  • Summer: SAE 30 (up to 30° C).
  • Winter: SAE 5W (up to -30° C).

Engine oil change.

Why regular replacement is necessary

Engine oil tasks:

  • lubricates,
  • cools,
  • cleans,
  • protects the engine from corrosion.

The lubricating film formed by the oil prevents the moving parts of the engine from rubbing against wear. In the worst case it will lead to complete engine damage. At the same time, the engine lubricant cools the parts and acts as a thin seal between the cylinder surface and the piston wiper. Dirt particles from the engine are collected in the oil filter until saturated. Then “dirty” engine oil becomes dangerous for the engine.

Engine oil and filters must be changed every 12 months or 10,000 km.

However, individual driving conditions and the associated increased engine load may affect the recommended replacement interval.

Engine oil is usually cheaper in a store than in a car service.

How to replace engine oil by yourself

Changing engine oil is not as difficult as it seems, especially on cars of domestic manufacturers.

You need:

  • the right oil,
  • tool,
  • funnel,
  • a measuring cup, and strong arms.
  1. To make it easy to remove waste oil with dirt particles, the engine should be warmed up before changing.
  2. Then the car should be parked so that it is accessible from below (for example, over a pit or on a lifting platform.
  3. You may need to remove the protection of the car’s crankcase. It is better to know about this in advance and prepare the tool.
  4. Unscrew the drain bolt on the engine crankcase.
  5. Oil will start to drain quickly. It may take some time until the waste oil is completely drained. So at the same time, it is suggested to remove the oil filter with a oil-filter key and remove it along with the old rubber seal.
  6. Cover the new rubber gasket with oil and tighten the new oil filter manually. If the waste oil has drained, the new engine oil can be refilled, preferably using a measuring cup to accurately indicate the amount of oil specified in the car’s user manual.
  7. After filling the oil cap is screwed in and the engine is allowed to distribute oil for a short time.
  8. Then we check the oil level. It is important to dispose of waste oil.

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