yeah don't use teflon tape it usually heats up and goes away or loses its hold especially on water stuff. tried it myself and learned the hard way. Use a thread sealer that is designed for radiator/water stuff or use J/B weld if you never plan on taking it out again. Remember DON'T use J/B weld if you want to remove or service it in the future. go to an autoparts store and get the right stuff.