What are you not telling us? This is like
http://ecomodder.com/forum/showthrea...ack-26505.html where the question was posed in it's simplest form, then it turns out he was asking about a motorcycle. What are you designing?
Lacking that about all one can say is the radiator needs a streamlined inlet duct before it *and* a streamlined exhaust duct after. The openings can be about 1/6th of the radiators cross-section. Inlet higher, at the (high static pressure) stagnation point, and exhaust farther back at 115° from the stagnation point. Use Coanda nozzles to cause the hot, pumped air to re-attach overall flow to the afterbody.
What else would you like to know.