What is this connection?

[Leeztruk]

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

 

[0xDEADBEEF]

I don't know what it's for, but I don't see why you couldn't use it. It looks like it's kind of right at the water level, which should be fine.

 

[someotherguy]

Return line from the heater core, depending on year model. Some have it go back to the water pump instead.

My '93 had a temperature sender in it that I think may have been for the aux fan, but was no longer connected.

For figuring out the size and threads, you've got the sample to measure right there, the plug.

Richard