Horse manure. If you took an all iron engine, what you are saying is the iron WOULD NOT BE ABLE to transfer heat into the coolant. What this implies is that the IRON engine would run hotter, because it would not be able to reject the heat.
What are you going to claim next, that the iron radiates it's heat into the air?
If the aluminum rejects more heat into the coolant, all this means is that the engine is going to run COOLER because it is getting rid of more heat that "was" in the engine. If it actually runs hotter, this is because the cooling system is too small.
Aluminum does not produce heat. What goes on in the combustion chambers does.
I'm no expert on theoretical thermodynamics, but I did spend not quite 15 years in the HVAC / R repair / maintenance field.