What Happens If You Put Too Much Coolant in a Car?

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The buildup of pressure caused by adding too much coolant to a car can cause the rupturing of hoses, internal pipes and even the radiator. When coolant is added to a car, it is cold, however, while the engine is running, the liquid starts to expand, causing a buildup of pressure. If the radiator is too full, this buildup of pressure is often too great for the internal workings of the car.