Preheat grill to medium, between 350° and 375° Fahrenheit.
Once grill is preheated, lay 8 large ears corn on grill grate over indirect heat. Grill corn 10 minutes, flipping ears of corn occasionally to grill all sides evenly.
Once ears of corn have charred slightly on all sides, carefully remove corn from grill and set aside to cool slightly.
When corn is cool enough to handle, stand one ear upright in large bowl. Position sharp chef's knife at top of corn ear and carefully push knife down corn cob, slicing kernels away from cob. Repeat on all sides of each ear of corn. Discard corn cobs.
Add ¼ cup melted butter, 6 tablespoons mayonnaise, 2 tablespoons fresh lime juice, 1 cup crumbled cotija cheese, 3 tablespoons chopped fresh cilantro leaves, salt, and freshly cracked black pepper to small mixing bowl. Whisk ingredients together until incorporated.
Taste mixture and add mayonnaise or lime juice as desired to achieve preferred flavor and consistency.
When satisfied with flavor, pour mixture over corn kernels in large bowl. Gently stir mixture into corn until kernels are fully coated.
Sprinkle ½ teaspoon chili powder, ½ teaspoon garlic powder, minced red onion, and additional cotija evenly over top over corn mixture. Serve immediately.