HEY ANDRE MICHAEL IS RIGHT ON THAT ONE , THE TEST PORT WILL NOT GIVE YOU A TRUE READING OF THE FLUID TEMP, IT WILL GIVE YOU MORE OF A CASE TEMP READING THAN ANYTHING , IT SHOULD BE IN THE COOLER LINE, AND THE FITTING SHOULD BE DEEP ENOUGH TO GET THE TIP OF THE PROBE DOWN IN TO THE FLUID FLOW IF POSSIABLE, EVEN A TINY BIT WILL MAKE IT MORE ACCURATE, ALLSO ONCE YOU GET IT WORKING CORRECTLY, WRAP THE COMPLETE BRASS T FITTING WITH WHAT IS CALLED CORK TAPE ,TO INSULATE IT FROM AIR MOVEMENT AROUND THAT AREA ,,CORKTAPE IS THE BLACK STICKY STUFF USED AROUND AUTOMOBILE A.C. LINE CONNECTIONS . JERRY