What causes excessive coolant in resorvoir?

Excessive coolant in the reservoir can be caused by a few factors, such as a faulty radiator cap that fails to maintain proper pressure, leading to overflow. Additionally, a malfunctioning thermostat or a leaking head gasket may cause coolant to leak into the engine, resulting in an overfilled reservoir. Lastly, improper coolant mixture or overfilling during maintenance can also contribute to this issue. Regular checks and maintenance are essential to prevent these problems.