Could be radiator cap, top hose is a bit stuffed, or top-tank of radiator is leaking. Hopefully the problem is in that order because that's cheapest to most expensive.

Look around the hose end, cap seat and top-tank mating point to see if there's any dried coolant.


Caps are cheap, can probably get one for like $15. Hose is about $40 new from Honda I think, but if it's just a little split at the end you could try removing it from the radiator neck, cutting off the end to above the split, and put it back on (DON'T tighten the clamp it anymore than 1/4 turn past 'firm' as the neck might crumble if it's brittle from age/heat exposure). Top tank + replacement + radiator clean/flush will set you back like $300-400 at a radiator shop.