[Diesel_Dave]

Don't forget that you can get buildup on the inside of the radiator as well. You can get rid of some of that by doing a coolant flush and refill.

It's also not fair to assume that the grille opening has to be as large as VW designed it to be. VW designed it to withstand the absolute worse-case scenario: loaded to the max weight rating, in high ambient temperatures, with low vehicle speeds, etc.

Most hypermiling & ecomodding techiques will decrese the cooling requirements because the engine won't be burning as much fuel. I've noticed that P&G, especially EOC P&G affects the time it takes my engine to warm up (an indication of the required cooling requirements after it's warmed up). I estimate that, for me, it takes almost twice as long to warm up with EOC P&G vs normal driving. The reason for this is twofold. First, I'm burning less fuel more efficiently, so there's less heat that needs to be taken away. Secondly, the engine cools down during the EOC portion. After a particularly long glide, I'll notice that my coolant temp gauge moves off it's normal operating temp.