Only to the extent that the extra water will absorbe a greater amount of heat than before - once its hot you still need to cool it down.

Air flow is the key - hence modern cars having rads that are totally boxed in. With many BMWs they use both a electrical fan AND a mechanical fan due to both the number of rads (water, air con, oil etc etc) and the requirment for air flow even when traveling slowly or with hot ambiant conditions.

I can't offer many solutions as I havent styarted my LET mini project yet. But I will face the same problems you do.

So far I am considering put the rad flat in the boot and scooping air from under the car up and out the boot lid itself. BUT I don't need to consider aero-dynamics greatly, its a brick to start with!

Alex