WD40 is a commonly used lubricant in many automotive applications, but it shouldn't be sprayed into the spark plug hole of a car. This is because WD40 is classified as a solvent, meaning it has the tendency to wash away the oil that coats your car's cylinder walls and create a difficult situation for the engine as it won't have enough lubrication. A better alternative would be to spray carburetor cleaner into the spark plug hole instead of WD40. This will help to break down any debris or dirt buildup in the area, and then compressed air can be used to blast it out from the spark plug hole afterward. Doing this will keep your car's engine running smoothly and make sure it's running as efficiently as possible.