Hi Keith when I got one for my 91 I got it from here not cheap but dose the job http://www.nomadracing.com/catalog/index.php?cPath=57&osCsid=9713c919e0772b82042087ed09a54997
Testing them in boiling water isn't really right you need to have a thermo in there to get it to the right temp to see if it opens when it should could be opening at boiling point which is to late if its in the engine you see where I'm coming from
Got to be your stat mate I took mine out and it stayed hot on the bottom hose I'm going with my rad and cap being fooked sent my new rad off today to be sorted then ill no it that was my problem.