How to Seal a Radiator Tube to the Housing With Silicone

Close the inlet and outlet flow valves on the body of your radiator.

Loosen and remove the radiator from the liquid lines connected to the valves you closed in Step 1. Use an adjustable wrench to loosen and remove the flanges after (inlet) and before (outlet) the valves.

Identify the loose radiator tube inside the inlet or outlet flanges on the radiator. Scuff the outside surfaces of the radiator tube and the inside surfaces of the housing with a sheet of 200 grit sand paper. This will provide a better surface for the silicone to adhere to.

Clean the outside surface of the radiator tube and the inside surfaces of the housing with a cloth soaked in isopropyl alcohol to remove any metal residue, dirt or oil.

Load the silicone caulking tube into the gun, cut off the tip of the caulking canister using a utility knife and advance the plunger of the gun to begin dispensing the silicone caulking. Apply caulking between the outside surfaces of the radiator tube and the inside surfaces of its housing to secure it in place. If it is very loose, support it while the silicone dries and firms up using a suitably sized wooden block to center the radiator tube in the center of its housing.

Allow 12 hours for the silicone to cure and firm up before reattaching the radiator to the inlet and outlet valves. Then open the valves and test for proper functionality.