Below is an illustration that shows an approximation of the temperature gradient on the radiator with the stock water-flow direction and radiator hoses. Note how the hotter part of the radiator (top) is where the cooler air coming through the top grille comes in, while the cooler, lower part of the radiator is where the hotter air exiting the intercooler passes through the radiator. Because the water exiting the radiator is nearly the same temperature as the air entering the bottom of the radiator, this setup can render the lower half of the radiator ineffective in hot climates.