Oil change, on a Morris Minor, but the principle is the same on all cars. It is best to have the engine warm for the oil to flow easily. The oil in good condition acts by providing a macroscopic film between the friction surfaces and does not shear under pressure. Dilution of the oil can occur from non-atomized gasoline droplets passing through the piston rings, for example when the choke is removed unnecessarily. This low-tech, old-technology detergent oil carries contaminants into the oil filter that must eventually be changed. The SAE30 oil is also available for these old engines. From my experience, the new oil of a better brand can even calm the engine. The used oil can be used to lubricate the road springs of the back leaf and can also be painted on the metal of the undereal / underbody to prevent rust! . Modern engines have different requirements.
Video credits to thomasking55 YouTube channel