[Rick Norwood]

The plastic radiator tanks are notorious for leaking on the frame side, (where it mounts to the front grill) just opposite of the upper radiator hose. In other words, where the Hot coolant hits the back of the plastic tank when it leaves the upper hose.

The radiator pressure tester can usually borrowed from your local Autozone for free. Pump up the Radiator when it is cool to the same pressure as the Radiator cap. You should be able to spot the leak easily. When My radiator started leaking, I had to loosen the radiator mount and move it away from the frame a little bit and the 3 inch long crack became plainly visible, and leaked like hell under pressure.

To buy yourself some time if you do have a leaking core, you can always buy a small plastic jumper for a couple of bucks that accommodates the two different sizes of heater hose and "jumper" them together by removing both hoses at the fire wall and using the clamps you just loosened to clamp the jumper in place. You won't have any heat, but it is Summer time and you can run this way until your wallet recoups.