If your Yamaha R15 V4 is suddenly overheating, you may be able to cover this issue under warranty, but it depends on the specific circumstances. It is recommended to visit the nearest authorized Yamaha service center for a thorough inspection. Overheating can be due to various reasons such as a malfunctioning radiator fan, low coolant levels, or blockages in the cooling system. If the issue is found to be a manufacturing defect or a problem that arose during the warranty period, it is likely to be covered under warranty. However, if the overheating is due to neglect or improper maintenance, it may not be covered.