Radiator repairers - solder?

Thanks guys. This was the 3 core deal have on my running stand and it was a couple tubes I broke plowing up to it. I used solid core tin & regular flux for sweating copper. I have a MAP gas torch and heat wasn't an issue, but it didn't flow well. Makes sense that acid core would be better. I normally fix anything I cam, but wouldn't think of retanking or recoring. We have a guy here who's good so he's doing my 65s V8 radiator for me.