When coolant degrades, the additives that inhibit corrosion in the cooling system begin to deplete. Once those additives are exhausted, the coolant becomes acidic and starts to corrode system components, such as the water pump, radiator, and thermostat. Even the slightest buildup of these materials on heat transfer surfaces prevents proper circulation, drastically affecting the engine’s ability to shed heat. Service involves flushing out old coolant with new coolant and a BG protectant.