There is a connection on my radiator, above the ATF upper line and below the coolant overflow connection, that is threaded and capped. What's it for? And does anyone happen to know what the thread size and pitch might be? I'd like to use this for my LS bleeder line, which is currently spliced into the upper radiator hose. The radiator in question is for a 350 engine application, in my '89 C1500. Thanks