Which of the following properties of oils helps in preventing spark plug fouling?

Dispersancy is the property of oils that plays a critical role in preventing spark plug fouling. This characteristic allows the oil to effectively suspend contaminants and particulates within the engine. As the oil circulates, it keeps these impurities dispersed rather than allowing them to accumulate and settle on surfaces, such as the spark plugs. This is particularly important in engine operation, as deposits on the spark plugs can cause misfire, poor ignition, and overall engine performance issues.

Through its dispersant properties, oil can manage and control soot particles and other combustion residues, preventing them from forming solid deposits on the spark plugs. By maintaining a cleaner environment within the combustion chamber and on the spark plugs, dispersancy contributes to more effective ignition and engine operation.

The other properties listed are beneficial for different reasons but do not specifically target spark plug fouling. Oxidation stability helps to prolong the lifespan of the oil by preventing it from breaking down, while a high viscosity index ensures that the oil maintains its viscosity over a range of temperatures. High ash content, on the other hand, can lead to increased deposits and potential fouling, making dispersancy the most relevant property in this context.