Unless there is a problem that causes the radiator cooling system to max out with the thermostat fully open at all times, I doubt venting the hood will make a difference in coolant temperatures. At least, they don't for me.
In my vehicles, none of which have grill blocks because in my semi-tropical climate I often need all the cooling I can get, the coolant temperatures are regulated by the thermostat at an optimal operational level. The addition of hood louvers have not changed that at all for me, and I really didn't want it to because temperatures below optimal can cause other operational difficulties, including a potential hit on fuel mileage.
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