Found my dads original 1971 duster!

Hissing is not normal. You probably need a new cap. The water temp sending unit is just for a small block Mopar. Teflon tape should be used.
Ok. Thanks! I’ll take rad cap in to the parts store. Also, if I grab an infrared thermometer, where would I check temperature? On the big rad hose or on the water pump? Where is it best to aim it? I’m hoping can get my temp gauge working, but if I can’t I’d at least like to know that it’s not overheating