If the engine is not at proper operating temperature, it'll burn more gas due to poor fuel atomization. The engine actually uses the heat in the combustion chamber along with the obvious to ignite all of the fuel.

This could also lead to engine knock and the ECU could retard your timing as well resulting in loss of power.

I agree with above comments, 99.99% is that your thermostat is stuck in the open position. Your coolant is constantly being circulated within the engine and with that big Koyo Radiator keeping enough of the coolant so cold, your engine doesnt have time to warm up.

With a bigger radiator, you may also want to go up 10 degrees on the thermostat from the factory specs OR less you plan on boosting or anything, then go back with the original temp.