Technician A says that spark knock can be caused by excessive scale in the cooling system. Technician B says that spark knock can also be caused by using fuel with a too-high octane rating. Who is correct?

To analyze the situation regarding spark knock, it is important to understand what spark knock actually is. Spark knock, also known as pre-ignition, occurs when the air-fuel mixture ignites prematurely in an engine cylinder before the spark plug fires. This can lead to engine knock, which can cause damage over time.

The assertion that excessive scale in the cooling system can lead to spark knock is valid. An overheating engine, often a consequence of a cooling system malfunction—such as scale buildup restricting coolant flow—can result in a higher operating temperature. This elevated temperature can compress the air-fuel mixture to the point that it ignites earlier than intended, contributing to spark knock. Therefore, the statement made by Technician A is accurate.

On the other hand, the claim that using fuel with a too-high octane rating causes spark knock is misleading. Higher octane fuel is generally designed to resist knocking, and while using an unnecessarily high octane fuel won't negatively impact most vehicles, it does not typically cause sparking knock either. In fact, vehicles designed for lower octane fuel that are instead supplied with higher octane fuel won't experience adverse effects directly linked to the octane rating.

Given this understanding, the information provided by Technician A is correct,