What's the best metal plug to screw in an aluminum radiator?

78elk

Dragway Regular
Mar 6, 2014
818
4
18
Mountain Home Id
What's the best metal plug to screw into an aluminum radiator? I installed a Cadillac transmission cooler and want to bypass the radiator. I need plugs to fill the holes where the lines are going now.
 

r_d_3

Daily Driver
Feb 25, 2020
34
3
8
24
New Jersey
If you get most of the trans fluid out you can probably just leave them open. Shouldn't be a problem.
 

r_d_3

Daily Driver
Feb 25, 2020
34
3
8
24
New Jersey
Thank you. What's the best way to get the fluid out?
probably pop the rad out and run your hose through the ports until no more trans fluid comes out, then the water will just evaporate, that's what i'd do at least.
 

78elk

Dragway Regular
Mar 6, 2014
818
4
18
Mountain Home Id
Thank you. I really don't want to take the radiator out. I probably should try to get the fittings first. I may need to come back and use the radiator transmission cooler with the Cadillac external cooler.
 

Killerdave8813

Dragway Regular
Jan 16, 2008
898
2
18
Cincinnati,Ohio
They make special brass plugs that will fill the trans cooler ports in the radiator, available at about any auto parts store, tell them you need a plug for a female 5/16" flare fitting in the radiator and what you're doing and they should be able to fix you right up, I have them in my cars as they're both standard trans, KillerDave
 

Killerdave8813

Dragway Regular
Jan 16, 2008
898
2
18
Cincinnati,Ohio
I wouldn't be too concerned about that, Brass and Aluminum are both non-ferrous metals and shouldn't react to one another adversely, now steel plugs might cause a problem but then again I'd bet your original cooler lines are steel and I imagine the fittings on those lines are steel as well, If you're that concerned wrap some teflon tape around the treads before you install the plugs