I have a heat exchanger leaking internally. It seems like from only one passage. Has anyone ever plugged a tube off? If so what did you use? Just trying to get this thing to hold coolant for a few more months to test the engines out.

Yes I know I can just fill the system with water and keep adding, and I will for now if it comes to that. Just a thought.

Any luck repairing heat exchanger?

I used a product made by US Chemical called Allmetal.

Thank you! So you just used the Allmetal and no wooden dowel? Also, curious how you prepped the tube since your seems to have held up.

Yep, still good to this day. Just Allmetal. I used a rifle bore brush and brake cleaner to prep the tube. .17 caliber brush IIRC. Taped off surrounding tube's. Used small screw driver to push allmetal into tube on both ends of HE. Probably got 1/4 of filler into each end of tube.

I just went through this but I wasn't looking for a temporary fix... I tried silver soldering it but its a right PITA cuz it sucks all the heat away so unless your an expert at heat exchanger repair, I wouldn't bother trying that route... I've heard lots of people using a self tapping screw and jb weld to plug tubes successfully.
When you get around to replacing, I ended up getting mine from Lenco.. The owner was great to deal with and turned around in a week and was the cheapest I found to boot.

Yeah I heard not to even bother with soldering or brazing. I used this stuff by JB Weld called SteelStick. Sandpaper wrapped around a drill bit to clean inside both ends. Got a 3/16 wooden dowel that fit perfect but tight in the tube and stuffed the putty in there with that about an inch or so, where it started building up inside instead of pushing in more. Let it cure, filled back with coolant and ran it! So far so good held pressure and no coolant loss.

I use that Steelstick a lot. Always performs well.