When does spark plug fouling caused by lead deposits typically occur?

Spark plug fouling caused by lead deposits primarily occurs when cylinder head temperatures are relatively low. In conditions where the engine operates at lower temperatures, such as at idle or during light power settings, lead from the fuel does not fully vaporize or burn away. This incomplete combustion leads to the accumulation of lead deposits on the spark plug electrodes.

When cylinder head temperatures are too low, the metal components do not reach the necessary temperatures to dissipate the lead adequately. As a result, these deposits build up over time, causing the spark plugs to foul. This can lead to poor engine performance, misfires, or difficulty starting the engine.

In contrast, when engines are running at higher power settings or at normal operating temperatures, the combustion process is more efficient, which helps to avoid the buildup of lead deposits. Similarly, unusually high temperatures can lead to other types of issues, such as pre-ignition or detonation, rather than fouling specifically from lead. Thus, maintaining optimal cylinder head temperatures is crucial for preventing spark plug fouling due to lead deposits.