When car owners change the oil; Everyone wants to lift the car high and drain the engine oil clean. Some car owners will still find that when adding oil, there is often some left over from a bucket of new oil that cannot be added. The amount left varies among different cars, with some having more or less. Is that because the 4S store didn't drain the oil thoroughly?



There are two reasons for this issue:



Firstly, no matter where the oil is changed, it naturally flows out by gravity. Due to the angle of the oil outlet and the irregular structure of the oil pan, there is always a portion of the oil that cannot flow out naturally. Due to prolonged use of engine oil, there are many impurities that cannot be completely drained. For example, if you put sand into a large basin of water and drill a hole at the bottom of the basin, you will find that there is always a portion of water and sand that cannot flow out. The same goes for engine oil. When you open the oil pan, you can see that there is still some oil on the crankshaft and connecting rod, which cannot be drained clean by gravity. Moreover, when the 4S store is quite busy, they won't give you engine oil for a long time, so if you have more old oil, you will add less new oil. So it's normal to have a little engine oil left.

There are also many ways to lubricate the engine, and some parts cannot rely on oil passage lubrication due to mechanical construction. They can only rely on the crankshaft balance weight and the continuous circular movement of the connecting rod bottom to splash oil into the lubrication area, such as the valve, top pillar, cylinder wall, etc. If all are cleaned, it will actually damage the engine during startup.



Secondly, there are some unscrupulous masters who do not drain the engine oil thoroughly and sell the remaining engine oil, causing 4S stores to turn a blind eye. There are only two options for buying engine oil: 1L or 4L. For example, for Passat and Magotan, if you add 4.8L, there is still 200ml left, and the extra 200ml will be kept. If you happen to have 5 Passat cars for maintenance today, it won't just add up to 1L, and you'll suddenly have one bottle. If you change the speed, just two cars can make up 1L. So, do you feel some knee pain from car owners who drop their keys for maintenance at the store without looking at them? Then the extra 1L can be sold, but not all car repairers are like this, after all, it is a minority.



Is it possible to damage the engine if the engine oil is not drained thoroughly?



As mentioned above, oil cannot be drained clean by gravity. Whether the remaining old oil will damage the engine is the concern of car owners. In fact, everyone doesn't have to worry at all. Engine oil has functions such as cleaning, lubrication, cooling, anti-corrosion, and sealing. Metal debris generated by internal wear and tear of the engine can be retained in the oil pan as the oil circulates. The oil pan oil pump filters the oil while conveying it to the upper part of the engine, and then the oil enters the lubricating oil channel, so there will be no damage to the engine interior.



During engine operation, engine oil is affected by the temperature of fuel combustion and the catalytic action of various media and metals, gradually deteriorating and aging, producing various harmful substances such as carbon deposits, paint films, and sludge that are harmful to the engine. Therefore, it is necessary to regularly clean the lubrication system and residual oil to ensure the "health" of the engine!



So how to store the remaining oil?



Reason for oil deterioration: Moisture: Under normal circumstances, the water content in the oil is below 0.03%. When the water content exceeds 0.1%, the additives in the oil will become ineffective, accelerating the oxidation process of the oil. The organic acids generated by engine oil oxidation and the acidic oxides in engine exhaust react with water to generate inorganic acids. These acidic substances increase the corrosion of the engine.



Then there is oxygen: oxygen also affects various additives in engine oil, and don't think that only good engine oil additives are abundant. There are additives in every engine oil. Especially under sunlight or high temperatures, the oxygen in the air reacts more quickly with engine oil.



There are also impurities: impurities mainly affect the cleanliness of the engine oil. When impurities are mixed in the engine oil, they can affect the lubrication effect of the engine oil, even lead to abnormal engine wear, thereby affecting its sealing performance, and even burning the engine oil.

If the owner fills the vehicle with this deteriorated oil, the components that need lubrication and cooling in the engine will not be adequately protected, and the load and wear of the engine will intensify, ultimately causing engine damage and leading to early major repairs.



Saving method:

1. Cover the oil bottle with a layer of plastic film, and then screw on the oil bottle cap. Pay attention to maintaining the sealing of the bottle mouth, choose a thicker plastic film, and then drip wax to seal, otherwise it will be difficult to isolate the air.

2. Place the sealed engine oil in a cool and dry place to avoid oxidation reaction and deterioration, such as in the corner of a wall. Of course, many car owners prefer to keep it in the trunk, which is also acceptable for emergency use.

3. Oil that has been sealed for a long time will inevitably contain moisture and impurities, and it must not be shaken before use. When adding engine oil, do not pour it all in. There may be a small amount of water or impurities at the bottom of the bottle, which can affect its performance and even have adverse effects when added to the engine. So add engine oil to keep a small portion of the bottom of the bottle, leaving all water and impurities in the bottle!



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