Ah, gotcha. Well, if it's not a thermostat housing or engine head, it's probably a hose. I dunno if you want to try some 'stop leak'?
http://www.amazon.com/Bars-Leaks-HDC-Radiator-Tablet/product-reviews/B000KKND3Q
http://www.amazon.com/Bars-Leaks-HDC-Radiator-Tablet/product-reviews/B000KKND3Q