Extra grill shutters are not necessary since the coolant flows only through the radiator once the engine reaches a certain temperature. So if you drive in really cold weather the thermostat won't open the flow through the radiator cycle anyways. Coasting downhills uses more gas than leaving the car in drive...while coasting, your engine idles and uses gas....when you leave it in gear, the engine doesn't use any gas by design. Just google it for details.