A decrease in coolant level in your motorcycle, such as the NS 200, after riding 180 km could be indicative of a coolant leak or an issue with the cooling system. It's important to investigate and address this problem to prevent potential engine damage from overheating.
Here are a few possible reasons for the coolant level drop:
Coolant leak: Check for any signs of coolant leaking from the radiator, hoses, water pump, or other components of the cooling system. A leak could be causing the coolant to escape, leading to a drop in the coolant level. Look for wet spots or puddles underneath the motorcycle after it has been parked.
Faulty radiator cap: The radiator cap helps maintain the correct pressure in the cooling system. If the cap is faulty or not sealing properly, it may allow coolant to escape, leading to a decrease in coolant level. Inspect the radiator cap for any visible signs of damage and consider replacing it if necessary.
Air pocket in the cooling system: If the cooling system wasn't properly filled with coolant or if there was an air pocket trapped within, it can cause fluctuations in coolant levels. This can result in a temporary drop in coolant level after riding. Ensure that the cooling system is properly bled and filled with the recommended coolant.
Overheating: If the engine is running too hot, it can cause excessive coolant evaporation, leading to a decrease in coolant level. Check if the motorcycle's temperature gauge indicates any overheating issues. Overheating can be caused by a malfunctioning thermostat, a clogged radiator, or other cooling system problems. Consider having the cooling system inspected by a professional mechanic.
It is advisable to consult a qualified mechanic or take your motorcycle to a service center to diagnose and address the issue properly. They will be able to perform a thorough inspection and identify the specific cause of the coolant level drop in your NS 200.