Radiator questions

[CountyLineGarage]

I’ve got a 95 k1500 Sierra that I need to put a radiator in. I’m not pushing anything crazy so a stock rad will do but does anyone know what the little tube coming out of the radiator running underneath the overflow line is. It’s capped off redneck style right now because the stupid rubber cap dry rotted off.
I’ve seen some rads with and some without that and wondered what they run it to and I’ve also got an aftermarket trans cooler added on with some Mickey Mouse rubber line going on and wondered if I actually need that or if the trans cooling lines going into the radiator are enough.

 

[sntrym]

The rubber cap covers a hole that can act as an inlet on some vehicles. The inlet can come from the heater core or somewhere else coolant exits from the system and needs to go back to the radiator. For a stock swap, just leave the cap on.

 

[sntrym]

Trans cooler is there proabbly because the PO was towing and needed it. If you don't tow, you won't need it.

 

[454cid]

GM put the return line from the heater core on the radiator some years/engines. My 99 454 has it connected to the radiator, for instance. I think the aftermarket just puts the port there no matter what, so they can use one radiator for multiple applications.

Those rubber caps are known for rotting out. I've heard the silicone caps are better.

 

[df2x4]

^ X2. Put a 5/8" silicone cap on it and call it a day. HPS makes some but they're expensive, like $14 a piece. If you're OK with buying from China you can find them on eBay for much cheaper in all different colors.