Overfilling coolant in your car can cause potential damages, including electrical damage, if the excess coolant comes into contact with engine wiring. The coolant tank is designed to accommodate the natural expansion and contraction of coolant, so overfilling it can lead to pressure build-up and cause the coolant to expand and contract improperly. Most of the time, excess coolant is expelled from an overflow hose, but if this doesnt happen, it can cause damage to the hoses and engine. Overfilling the coolant tank can also lead to air pockets in the engine, which can cause the engine to overheat and damage it. If you overfill your coolant, its best to address it immediately to avoid any possible electrical damages. Ideally, you should stop at a local auto shop and have the excess coolant removed from the system. Its important to note that you should never fill up the coolant in a car after driving and the engine is still hot. Let the car cool down before adding a fresh top-up of coolant.