We would need to look at the situation to know the effectiveness. We need to know temp in and out of the IC core, both with the without the water spray.

If you live in a humid climate, and have a large IC, then the effectiveness will not be as high shooting water on the outside. If you have an undersized or heatsoaking IC, and lower relative humidity, a little water is very effective. For normal street driving with a larger IC, the results are not as dramatic.

You can inject into the plumbing on the hot side of the IC, but again, it depends on the heat load.

Data is the key to knowing what will be effective and what mat be marginal.