Lubricating and reduce the wear of engine : between the piston and cylinder ,main shaft and bearing bush existing rapid relative sliding,to prevent the over wear of parts, it is necessary to build oil slick between two surfaces.Having enough thickness of oil slick to seperate the parts in order to reduce the wear of parts.
Cooling and decrease the temperature: engine oil can bring the heat back to sump and emit out to air and help water tank cooling the engine.
Cleaning :good engine oil can circulating the carbide ,fatlute,prill over the engine parts to the sump,through the flow of lubrication oil ,cleaned all dirty staff over the parts.
seal and prevention of leakiness, engine oil can form a seal ring between the piston and piston ring,reducing the leak of gas and entering of contaminated things.
Prevetion of rust and corrosion :lubrucation oil can attach to the surface of parts to prevent water ,air ,acidic substance and harmful gas get in touch with parts.
decrease the vibration and buffering : when the cylinder port increase the pressure rapidly ,suddenly will put up the pressure to piston ,piston crumbs,connecting rod,the bearing of crankshaft,this pressure through the lubricating of bearing ,let the impact and pressure to function as buffering .