3. Cooling system: Generally composed of water tank, water pump, radiator, fan, thermostat, water temperature meter and water release switch;
4. Lubrication system: The engine lubrication system consists of an oil pump, water filter, oil filter, oil passage, pressure limiting valve, oil gauge, sensor and dipstick;
5. Fuel system: The fuel system of a gasoline engine consists of a gasoline tank, a gasoline meter, a gasoline pipe, a fuel filter, an oil pump, an air filter, an intake and exhaust manifold, etc.;