What is the reason for bubbles in the engine oil when pulling out the dipstick?

[DelBeckett]

The reason for bubbles in the engine oil when pulling out the dipstick is the mixing of air, which is a normal occurrence. The engine oil is agitated by the crankshaft in the crankcase, inevitably causing air to be mixed into the oil. This air forms small bubbles in the oil, and due to the oil's viscosity, these bubbles do not immediately disappear or burst. Below is a detailed explanation of the hazards of air bubbles in engine oil: Overview: Bubbles and foam are harmful to both the lubricating oil and the machinery. Bubbles accelerate the oxidation and deterioration of the lubricating oil, speed up the consumption of additives, affect heat dissipation, prevent the formation of a complete lubricating oil film, and cause wear to the equipment. Others: Air is easily compressible. When there is air in the lubricating oil, the oil film thickness becomes thinner or even breaks, leading to direct friction between mechanical parts and resulting in wear.