Can I switch from 40 oil to 30 oil?

[OAva]

It is possible to switch from 40 oil to 30 oil, but the condition for switching depends on whether the engine can use 30 oil. If it can, then the switch is possible; if not, then it cannot. The numbers 30 and 40 refer to the high-temperature viscosity of the oil, with 40 oil having a higher viscosity than 30 oil. The functions of engine oil are: 1. To separate the surfaces of relatively sliding parts such as pistons and cylinders, main shafts and bearing bushes, reducing wear on components; 2. To carry heat back to the oil tank and then dissipate it into the air, helping the radiator cool the engine; 3. To carry carbon deposits, sludge, and worn metal particles from engine parts back to the oil tank through circulation, cleaning the working surfaces of the parts; 4. To form a sealing ring between the piston rings and pistons, reducing gas leakage and preventing external contaminants from entering; 5. To adsorb onto the surfaces of parts, preventing water, air, acidic substances, and harmful gases from contacting the parts; 6. To cushion impact loads on pistons, piston rings, connecting rods, and crankshaft bearings.