When boiling out a cylinder block, why is it critical that all the scale in the water jacket be removed?

When boiling out a cylinder block, it is critical to remove all the scale in the water jacket because scale acts as an effective insulator. When scale accumulates within the water jacket, it prevents proper heat transfer. The coolant is responsible for absorbing heat from the engine and carrying it away to maintain optimal operating temperatures. If scale is present, it creates a barrier that restricts the flow of coolant and diminishes its ability to absorb heat from the engine, leading to overheating and potential engine damage.

Understanding the implications of scale buildup emphasizes the importance of ensuring that the water jacket remains clear. This not only helps in effective cooling but also promotes the longevity and reliability of the engine.