I didn't say that it wasn't; I said that the math was *undermined*.

To explain: your calculations - correct as they may be - were based on a *theoretical *reduction in the amount of open area of each grille slot; no specific definition of "grille insert" was defined until much later in the thread. Without defining exactly how much blockage or lack of blockage a specific product may or may not create, no amount of calculation can attempt more than answering the most basic form of the OP's first question: "Do grill inserts affect airflow through the condenser and radiator?" I think that if anything, your calculation proves that grille inserts do, in fact, affect airflow...but without knowing exactly what product the OP had in mind, the second part of the question - "Would it cause the AC to not work as well, or the engine to overheat?" - cannot be accurately answered. Any given grille insert could offer either more, less, or the same amount of reduction in airflow that your calculations assumed... so even though the numbers you posted strongly suggest that most inserts will have no meaningful impact, they cannot be extrapolated to prove the impact or non-impact of an as-of-yet unnamed and unmeasured product. In that light - and to address your last comment - the math may or may not be the same; it all depends on exactly what kind of reduction any given product offers.