A much better solution would be to scrap that idea and look into fabbing up naca ducts on the fenders/body. You could in theory get rid of the entire grille opening on the front of the vehicle and only utilize the ducts for cooling. If it's good enough for a Ferrari, it's good enough to work on whatever you have.
Surface radiators, being so much larger, would be cooler than a common radiator. Radiators don't make a cloud of steam when a puddle splashes up into them...
1) Any surface hotter than 140 oF has to be guarded or insulated per OSHA regs.
2) Because surface area must increase as delta t decreases, the size and weight of a radiator designed for such low temperatures would become a liability rather than an asset.
3) There are conditions when steam would arise from an external radiator. Sitting in traffic in light rain would produce clouds over the hood. Not good for visibility or pedestrians.
Capitalism: The cream rises. Socialism: The scum rises.
I pointed out recently that waste heat is WASTED. The logical solution for the typical short trip driver.... commuter to work and grocery store... is to use a eutectic salts container in the trunk, and rather than trying to get rid of heat, try to save it to heat your house!! The percentage of the waste heat that comes from the radiator might be interesting to know.
Ceramic coatings can be applied inside the head and ports to reduce the amount of heat that is absorbed by the coolant. Cylinder walls are not the main source of heat, the head and exhaust ports are. Reducing heat absorption into coolant and forcing more of it out with the exhaust would reduce cooling drag.
Suppose you collect heat in your eutectic salt tank..... from coolant only, and don't need to heat your home with it. It could serve to heat the hot water you use in your home..... or it simply could be cooled while the vehicle was parked. Vehicles spend far more time parked than moving. Accumulate heat while driving, get rid of it while parked.
I am not a believe in dramatically increased fuel economy tricks...... They never pan out. I do believe that improved utilization of the energy through capturing heat is where the answer really lies. While your gas mileage may not improve, you save heating fuel, electricity, natural gas, propane, etc.