So I just received my dual row radiator from ebay ( http://www.ebay.com/itm/120964719063...ht_8186wt_1098 ) and everything seems fine besides the fact that there is an open hole on it that I am having trouble plugging. It is not threaded and I have no use for it so I need to find a way to cap it. My local Autozone and napa said they didn't have anything (which suprises me). O'reilly's had caps that looked thick enough but none in the right size. Has anyone else had this problem?

 

Are you talking about the hose nipple on the tank a few inches down from the radiator cap?
Mine was threaded and had a bolt with an o ring seal on it.
I bought one identical to your link, Champion 2 row.

I have bought rubber hose nipple caps in Napa or Autovalue, they usually come in several different sizes.

 

It is pretty far down from the radiator cap and there are other spots that are threaded, this one is not. I found a box of random sized caps at Oreilly's but none of them felt close enough to the right size even with a hose clamp on it.

I contacted the seller and they told me that it was a spot for a tempature sensor to go. My sensor doesnt go there and is a completely different size, so I still need something to cap it off.

Would welding it shut be a terrible idea? I'd hate to do it (I feel like its a half *** way to go) but I have a friend who can weld aluminum. I am going to try and get it threaded before resorting to welding.

 

looks like a radiator low sensor like used in the c4, ACDELCO Part # 10054615 SWITCH, LOW ENG COOL