If it blew the "Y" fitting, it's a problem that no amount of cooling additives, mixture, etc is going to change. It has to be either a blocked rad or a a warped head. If you look at the '83 head, Honda changed the design considerably, added extra head bolts and rearranged the pattern, all b/c they had experienced some problems w/ the head warping and causing overheating. If the head warps, you'll get hot, pressurized combustion gas adding heat and pressure to your cooling system -- not a good mixture.
My rads did not look bad, but when one started leaking and I took it to a rad shop to be fixed, they found it was pretty blocked up. Getting the rads rodded out fixed about 90% of my issues. Getting the head trued took care of the rest.
Remember, 1982 was only the 2nd year for watercooled 250s from Honda. They were still working on getting the bugs out. Add 25 years of age to your bike and you've got some work to do to keep it running well.