hit the parts store and buy a rad dye leak kit. you add like 10 drops to the rad, drive around for a bit. then with a some yellow glasses and a black light you can see the trail of coolant. some dont need the glasses or light. see what they sell.
if they dont have the dye kit
, then rent a coolant pressure tester, it fit the rad where the cap would go and you pump it up to 18 psi, its got a hand pump on it like bike tire pump. then watch for the leak, the pump shows pressure and you'll see it drop if its leaking, and this will force it to leak making it easier to find when the engine is cold.
