[QUOTE=i_am_socket;37889] Blocking behind the grill will likely give you an increase rate of engine heating which is a good thing, but that's a mechanical benefit and not so much an aerodynamic one.
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blocking the radiater will not give you an increased heating rate!!!
the water does not leave the engine untill it's HOT (unless you dont' have a thermostat, and if thats the case, you are asking for problems).