Is there a way to test a radiator outside of the car for leaks? I have an extra sitting around and have no clue how to pressure test it, especially since there are no cap fittings on the top of these things.

 

Cap all the access points to the radiator and thread a high pressure air line into one. Submerge the radiator in a tub of water, then pressurize the radiator.

If you get bubbles than you have a leak. No bubbles means no leak

 

My issue is the caps or lack of. I really cannot think of any kind of material to create a cap or seal the radiator outside of the car, without damaging it.

 

Get two silicone couplers, bolt one side to radiator and a plug to the other?

If you have a ratty old radiator hose that you can cut up than I figure that would work too.

Any half decent radiator shop should be able to do this for a minimal fee.

 

Thanks for the tip, Fendamonky, I should have just gone to a radiator shop in the first place.