No, not all motorcycle engines have radiator caps. The presence of a radiator cap depends on the cooling system design employed by the motorcycle manufacturer. Motorcycles can have different types of cooling systems, including air-cooled, liquid-cooled, and oil-cooled systems.
Air-cooled engines do not have radiators or a liquid cooling system, and therefore they do not require a radiator cap. These engines rely on air circulation to dissipate heat from the engine. Examples of motorcycles with air-cooled engines include many classic and vintage models, as well as some modern motorcycles designed for specific purposes like off-roading or cruising.
Liquid-cooled engines, on the other hand, have a cooling system that utilizes a radiator and coolant to regulate the engine temperature. These engines often have a radiator cap, which allows for the pressurization and expansion of the coolant as it circulates through the system. The radiator cap helps maintain the optimal pressure and boiling point of the coolant. Most modern motorcycles, especially those with higher engine displacements, utilize liquid cooling systems and will have a radiator cap.
Oil-cooled engines rely on engine oil to dissipate heat. They may have oil coolers or other means of maintaining the oil temperature, but they typically do not have a radiator cap specifically for the cooling system.
It's important to consult the specific motorcycle's owner's manual or reach out to the manufacturer to determine the cooling system type and whether it has a radiator cap.