I'm in the process of swapping a 6.0L LQ from a 2000 Silverado 2500 into my 85 crew cab. I'm making an offroad truck. The engine is backed by a th400 that I'm running 3/8 tube with flared ends to the 2000 Silverado 2500 radiator. I want to replace the quick connect but cannot figure out what the thread size and type the radiator is. I would like to convert to a 1/4 npt or a 3/8 tube inverted flare fitting. I'm trying to avoid the expensive an fittings and braided line as it is not a show truck. I have done ton of searching on google, pirate 4x4, here and more but cannot find an adaptor that works.

Thank for help in advance!

 

Not sure about the Silverado radiator, but on my TBSS, the radiator side quick connect fitting was a -6AN o-ring (9/16-18 thread). There's a thin washer behind the factory fitting that needs to be reused. The fittings/washers actually hold the cooler to the inside of the radiator tank. Without the washer to hold the cooler in place, it can move and cause a coolant leak on the tank. I tried using a standard flat washer first, but it was too thick and wouldn't allow the o-ring to seal on the cooler. The thinner washer from the factory fitting worked for me. Again, this was on a TBSS, not a Silverado, but yours may be similar.

 

It looks like the Silverado is a little different. There is a big thin nut that holds the cooler in place. I got my tube and tube nuts in last night. The 5/16"-3/8" tube nuts seem the thread into the cooler. I have attached some pictures the show the quick connect and the cooler side. The cooler side looks like it has the flare for an inverted flare tube nut. I will flare an end tonight and try this to see if will tighten up. It will be a while before I get front clip back on and radiator in place but like to have all the parts before I'm ready to put in. Has anyone else done this?

Thanks for the advise Skinny

 

Why not use the radiator for the '85? It will cool a LS engine just fine, I drove a 5.3L swapped '85 C20 Suburban for 10 years with the original 3-core "re-cored" radiator.

 

The main reason is so I don't have to purchase an engine oil cooler and make adaptors for it.