i can give you a quick tip that helped me find it in like 12 seconds. go get a uv dye detection kit. i know, its like 40 bucks for the fancy stuff and light, etc. if you have an LED flashlight, it will counteract with the dye, still turning it green, even in daylight. pour it in the rad, drive it around for a bit, open up thermostat, the norm...then pop the hood with it running and check it out. bright green clues where it leaks. thats who i found out my rad cap was at fault...
it also helps if you do this after dusk. real easy to spot.
