The automotive cooling system will have hardness present as a result of the water supplies used. This hardness along with the inhibitors in the antifreeze can lead to scale deposits forming, especially in high heat transfer areas. Corrosion products can also form and contribute to sludges in the coolant system. These deposits and sludges can reduce heat transfer, block radiators causing higher operating temperatures, and plug heater cores. Experimental tests were conducted to determine the effectiveness of different commercial antifreezes as scale and sludge inhibitors in a laboratory test boiler. The addition of an environmentally safe organic additive to a commercial antifreeze gives better scale inhibition on a high heat transfer surface than the same antifreeze without the additive. The amount of scale was determined and was analyzed.